ListEnumerable<T>

Show usages

Wraps a simple IEnumerable<T> into a IListEnumerable<T>.

Inheritance Hierarchy

ListEnumerable

Implemented Interfaces

IListEnumerable<T>

IEnumerable<T>

Remarks

This implementation is optimized for IList<T> and ICollection<T>, as well as Array<Object> IEnumerable<T>s.

This is a convertible type that can be used with the following notation(s) in parameter lists, parameter objects or setters.

It is possible to specify an Array or to use the native 'iterable' protocol, iterators, or generators to populate the ListEnumerable<T> instance:

// Array
object.property = [item1, item2]

// Iterables
object.property = new Set([item1, item2])
object.property = new Map([
  [key1, item1],
  [key2, item2]
]).entries()

// Generators
function* generator(i) {
  yield i
  yield i + 10
}

// via the iterator protocol (with invocation)
object.property = generator(10)

// via the generator function (will be executed immediately to populate the collection)
object.property = function* generateValues() {
  yield 1
  yield 2
}// Array
object.property = [item1, item2]

// Iterables
object.property = new Set([item1, item2])
object.property = new Map([
  [key1, item1],
  [key2, item2]
]).entries()

// Generators
function* generator(i: number) {
  yield i
  yield i + 10
}

// via the iterator protocol (with invocation)
object.property = generator(10)

// via the generator function (will be executed immediately to populate the collection)
object.property = function* generateValues() {
  yield 1
  yield 2
}

Note that when using native iterables, in contrast to IEnumerable<T> created with from which will reevaluate upon re-enumeration, the list will be populated only once, immediately after creation when created with from, and thus the generator will only be executed once.

Type Parameters

T: The type of the enumerable.

Type Details

yfiles module: core
yfiles-umd modules: All modules
Legacy UMD name: yfiles.collections.ListEnumerable

Constructors

ListEnumerable

()

Creates a new instance with a backing List<T> as the backing store.

ListEnumerable

(backingEnumerable: IEnumerable<T>)

Creates a new instance using the given backing enumerable.

Remarks

Note that even though the parameter is convertible to anything that can be converted to enumerables, using iterables is not recommended, because they will only be evaluated once. If you want to use generator functions, pass the function, directly. Still, this will potentially cause a lot of reevaluations so caching the output, once, via toList might be a good idea.

Parameters

options - Object
A map of options to pass to the method.

backingEnumerable - IEnumerable<T>: The enumerable to back this instance.

Properties

backingEnumerable

: IEnumerable<T>

Gets the backing enumerable.

size

: number

Gets the number of elements in this collection.

Overrides

IEnumerable.size

Methods

append

(items: T…) : IEnumerable<T>

Creates a wrapped enumerable that has one or several elements appended to it.

Remarks

In contrast to concat, this method will not treat the items any special if they are array-like or enumerable-like.

Parameters

options - Object
A map of options to pass to the method.

items - T: The item(s) to prepend to the enumeration

Returns

↪IEnumerable<T>: A new live view over the original enumerable that has each of the items appended to it.

Examples

const list = List.fromArray([1, 2, 3, 4])

const appendedEnumerable = list.append(5, 6)
console.log(appendedEnumerable.toArray()) // yields [1,2,3,4,5,6]

// show live updates
list.add(4.5)

console.log(appendedEnumerable.toArray()) // yields [1,2,3,4,4.5,5,6]

Overrides

IEnumerable.append

at

(index: number) : T

Returns the element at the given index in this enumerable.

Parameters

options - Object
A map of options to pass to the method.

index - number: The index of the element to return. Supports relative indexing from the end of the enumerable when passed a negative index. In other words, if a negative number is used, the returned element will be found by counting back from the end of the enumerable.

Returns

↪T: The element at the given index, or undefined if the index is not within the range of this enumerable.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4])
console.log(enumerable.at(0)) // yields 1
console.log(enumerable.at(-1)) // yields 4
console.log(enumerable.at(5)) // yields undefined

Overrides

IEnumerable.at

concat

(elements: Object…) : IEnumerable<T>

Concatenates this enumerable with the given other elements in a new dynamic IEnumerable<T>.

Remarks

The returned enumerable is dynamic, in other words, if elements are added or removed from one of the original enumerables, the returned enumerable changes, too. If you want to store the current state of the concatenation, create a list or array of it.

Parameters

options - Object
A map of options to pass to the method.

elements - Object: Rest arguments to be appended. In case the elements are enumerable-like, too, they will be will be enumerated after the others have been enumerated. But this can also be simple objects of type T in which case they will be appended to the enumerable just like with append

Returns

↪IEnumerable<T>: A dynamic composite enumerable.

Examples

const enumerable1 = IEnumerable.from([1, 2])
const enumerable2 = IEnumerable.from([3, 4])

console.log(enumerable1.concat(enumerable2).toArray()) // yields [1,2,3,4]

// single values can be used, too
console.log(enumerable1.concat(3, 4).toArray()) // yields [1,2,3,4]

// arrays are flattened
console.log(enumerable1.concat([5, 6], [7, 8]).toArray()) // now contains [1,2,5,6,7,8]

// works with arrays and array-like collections, too
console.log(enumerable1.concat([3, 4]).toArray()) // yields [1,2,3,4]

The returned enumerable is dynamic

const list1 = List.fromArray([1, 2])
const list2 = List.fromArray([3, 4])

const result = list1.concat(list2)

console.log(result.toArray()) // yields [1,2,3,4]

list1.add(2.5)

// result changed also
console.log(result.toArray()) // yields [1,2,2.5,3,4]

list2.add(5)

// result changed also
console.log(result.toArray()) // yields [1,2,2.5,3,4,5]

Overrides

IEnumerable.concat

distinct

(keySelector?: function(T):Object, thisArg?: Object) : IEnumerable<T>

Creates a wrapped enumerable that yields each element only once.

Remarks

To determine equality between elements, the logic of a HashMap<TKey,TValue> is used, i.e. the equals and hashCode methods are used for those elements that derive from Object.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

keySelector - function(T):Object

The optional function that determines the key to determine distinctness of the elements. If omitted, the element itself is used.

Signature Details

function(element: T) : Object

A function which creates a key for the given element.

Parameters

element - T: The element to get the key for.

Returns

Object: The key for the element.

thisArg - Object

The optional object to use for thisin the keySelector function.

Returns

↪IEnumerable<T>: A new live view over the original enumerable that yields each element with a given key at most once.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 3, 4])

const result = enumerable.distinct()

console.log(result.toArray()) // yields [1,2,3,4]

Overrides

IEnumerable.distinct

elementAt

(index: number) : T

Returns the element at the given index in this enumerable.

Remarks

This method is a precursor of the at method and can not yet handle negative indices. We recommend using the at method instead, as this method will be removed eventually.

Parameters

options - Object
A map of options to pass to the method.

index - number: The index of the element to return.

Returns

↪T: The element at the given index.

Throws

Exception({ name: 'ArgumentError' }): If the index is not within the range of this enumerable.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4])

const element = enumerable.elementAt(0)

console.log(element) // yields 1

Overrides

IEnumerable.elementAt

every

(predicate: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : boolean

Determines whether every element of the enumerable matches the given predicate.

Parameters

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if the element matches a condition.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪boolean: true if all elements of the enumerable match the given predicate, false otherwise.

Throws

Exception({ name: 'ArgumentError' }): predicate is null.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4])

console.log(enumerable.every((item) => item < 5)) // true

console.log(enumerable.every((item) => item < 4)) // false

Overrides

IEnumerable.every

filter

(predicate: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : IEnumerable<T>

Returns a dynamic IEnumerable<T> of the elements of this enumerable which match the given predicate.

Remarks

Parameters

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if the given element should be included in the resulting enumerable.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪IEnumerable<T>: A dynamic enumerable of the elements which match the given predicate.

Examples

const enumerable = IEnumerable.from([10, 2, 30, 4, 5, 6])

const result = enumerable.filter((item) => item < 5)

console.log(result.toArray()) // yields [2,4]

The returned enumerable is dynamic

const list = List.fromArray([10, 2, 30, 4, 5, 6])

const result = list.filter((item) => item < 5)

list.add(1)

// result changed also
console.log(result.toArray()) // yields [2,4,1]

Overrides

IEnumerable.filter

find

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : T

Returns the first element of this enumerable, the first element of the enumerable that matches a given predicate if specified, or null if there is no such element.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if the given element should be returned.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪T: The first element of this enumerable, its first element that matches a given predicate, or null if there is no such element.

Examples

const enumerable = IEnumerable.from([10, 2, 3, 9, 5, 6])

console.log(enumerable.find((item) => item < 5)) // yields 2

// no matches with the given predicate
console.log(enumerable.find((item) => item < 2)) // yields null

Overrides

IEnumerable.find

findIndex

(predicate: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : number

Searches the enumerable for the first item for which predicate returns true and returns its index.

Parameters

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if an item matches the search conditions.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪number: The index of the first item for which predicate returns true or -1 if there is no such item in the enumerable.

Overrides

IEnumerable.findIndex

findLast

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : T

Returns the last element of this enumerable, the last element of the enumerable that matches a given predicate if specified, or null if there is no such element.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if the given element should be returned.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪T: The last element of this enumerable, its last element that matches a given predicate, or null if there is no such element.

Examples

const enumerable = IEnumerable.from([10, 2, 3, 9, 5, 6])

console.log(enumerable.findLast((item) => item < 5)) // yields 3

// no matches with the given predicate
console.log(enumerable.findLast((item) => item < 2)) // yields null

Overrides

IEnumerable.findLast

findLastIndex

(predicate: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : number

Searches the enumerable for the last item for which predicate returns true and returns its index.

Parameters

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if an item matches the search conditions.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪number: The index of the last item for which predicate returns true or -1 if there is no such item in the enumerable.

Overrides

IEnumerable.findLastIndex

first

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : T

Returns the first element of this enumerable or the first element of this enumerable that matches a given predicate, if specified.

Remarks

The method find serves a similar purpose as this method and is more closely modelled on the Array<T> method. Consider using that method instead.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A function which returns true if the given element should be returned.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪T: The first matching element of this enumerable.

Throws

Exception({ name: 'InvalidOperationError' }): If this enumerable does not contain a matching element.

Examples

const enumerable = IEnumerable.from([10, 2, 3, 9, 5, 6])

console.log(enumerable.first((item) => item < 5)) // yields 2

// no matches with the given predicate
console.log(enumerable.first((item) => item < 2)) // throws exception

Overrides

IEnumerable.first

firstOrDefault

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : T

Returns the first element of this enumerable, the first element of this enumerable that matches a given predicate, if specified, or null if there is no such element.

Remarks

This method is obsolete. Use the find or at methods instead.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if the given element should be returned.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪T: The first element of this enumerable, its first element that matches a given predicate, or null if there is no such element.

Examples

const enumerable = IEnumerable.from([10, 2, 3, 9, 5, 6])

console.log(enumerable.firstOrDefault((item) => item < 5)) // yields 2

// no matches with the given predicate
console.log(enumerable.firstOrDefault((item) => item < 2)) // yields null

Overrides

IEnumerable.firstOrDefault

flatMap

<TResult>(selector: function(T, number, IEnumerable<T>):IEnumerable<TResult>, thisArg?: Object) : IEnumerable<TResult>

Returns a flattened dynamic IEnumerable<T> of this enumerable using the given selector function which returns an enumerable for each element of this enumerable.

Remarks

Type Parameters

TResult

Parameters

options - Object
A map of options to pass to the method.

selector - function(T, number, IEnumerable<T>):IEnumerable<TResult>

A function which returns an enumerable for each element of this enumerable.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : IEnumerable<TResult>

The selector to use for the IEnumerable<T>.

A function which returns a result of type IEnumerable<T> for each element.

Parameters

element - T: The current element create a result for.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

IEnumerable<TResult>: A result of type of TResult created from the element.

thisArg - Object

The optional object to use for this in the function.

Returns

↪IEnumerable<TResult>: A flattened dynamic enumerable of the enumerables provided for each element of this enumerable.

Examples

const enumerable = IEnumerable.from([1, 2, 3])

const result = enumerable.flatMap((item) =>
  IEnumerable.from([item, item * 2])
)

console.log(result.toArray()) // yields [1,2,2,4,3,6]const enumerable = IEnumerable.from<number>([1, 2, 3])

const result = enumerable.flatMap((item) =>
  IEnumerable.from<number>([item, item * 2])
)

console.log(result.toArray()) // yields [1,2,2,4,3,6]

The returned enumerable is dynamic

const list = List.fromArray([[1], [2], [3]])

const result = list.flatMap((item) => IEnumerable.from([item[0] * 2]))

list.add([4])

// result changed also
console.log(result.toArray()) // yields [2,4,6,8]const list = List.fromArray<number[]>([[1], [2], [3]])

const result = list.flatMap((item) =>
  IEnumerable.from<number>([item[0] * 2])
)

list.add([4])

// result changed also
console.log(result.toArray()) // yields [2,4,6,8]

Overrides

IEnumerable.flatMap

forEach

(action: function(T, number, IEnumerable<T>):void, thisArg?: Object)

Iterates this enumerable and invokes the given function for each element with the element, its index, and this enumerable as arguments.

Parameters

options - Object
A map of options to pass to the method.

action - function(T, number, IEnumerable<T>):void

The function to call for each element.

Signature Details

function(element: T, index: number, source: IEnumerable<T>)

An action to execute for each element of an IEnumerable<T>.

Parameters

element - T: The current element.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

thisArg - Object

The optional object to use for this in the function.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4])

enumerable.forEach((item) => console.log(item)) // 1 2 3 4

// accessing the index
enumerable.forEach((item, index) =>
  console.log(`Item #${index} is ${item}`)
)

Overrides

IEnumerable.forEach

get

(i: number) : T

Gets the i-th element in the collection.

Parameters

options - Object
A map of options to pass to the method.

i - number: the zero-based index of the item in this collection

Returns

↪T: the item for the given index

Throws

Exception({ name: 'ArgumentError' }): i is not a valid index in the IListEnumerable<T>.

Implements

IListEnumerable

getEnumerator

() : IEnumerator<T>

Gets an IEnumerator<T> which can be used to enumerate the items this instance represents.

Remarks

This is the low-level API that needs to be implemented by all enumerables. Clients will only have to use this API, rarely, as iteration is more conveniently handled by the forEach method or using the iterable (for(let item of enumerable){}) protocol.

Returns

↪IEnumerator<T>: The IEnumerator<T> which can be used to iterate over the items in this instance

Implements

IEnumerable

groupBy

<TKey,TResult>(keySelector: function(T, number, IEnumerable<T>):TKey, resultCreator?: function(TKey, IEnumerable<T>, number):TResult, thisArg?: Object) : IEnumerable<TResult>

Groups the elements in the enumerable according to the equality of a key.

Remarks

For each element in the original enumerable the keySelector will be used to retrieve a key. All elements with the same key will be provided to the optional resultCreator function that receives both the key, and an IEnumerable<T> of the elements that match that key to create a resulting object that will be yielded by this enumerable. Note that the resulting enumerable does not necessarily preserve the order of the (first) appearance of their elements in the original sequence. The elements of each group passed to the resultCreator are in the order of their original appearance.

Type Parameters

TKey: The type of the key elements.
TResult: The type of the created elements.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

keySelector - function(T, number, IEnumerable<T>):TKey

A function which selects from each element the key.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : TKey

A function which creates a key for the given element.

Parameters

element - T: The element to get the key for.
index - number: The index of the element in the underlying .
source - IEnumerable<T>: The underlying

Returns

TKey

resultCreator - function(TKey, IEnumerable<T>, number):TResult

An optional function which transforms each group of elements and their common key into a resulting object. If omitted, the default implementation will create arrays of length 2 where the first element is the key and the second element is an IEnumerable<TSource> of the elements with the corresponding key.

Signature Details

function(key: TKey, group: IEnumerable<T>, index: number) : TResult

A function which transforms a group of elements and their common key into a resulting object.

Parameters

key - TKey: The key of the provided group.
group - IEnumerable<T>: The group of elements with the given key.
index - number: The index of the group.

Returns

TResult: A resulting object for the given group with the given key.

thisArg - Object

The optional value to use as this when executing the keySelector and resultCreator .

Returns

↪IEnumerable<TResult>: An enumeration of groups of the original enumerable.

Examples

A simple groupBy example

const enumerable = IEnumerable.from([
  { type: 'A', amount: 1 },
  { type: 'A', amount: 2 },
  { type: 'B', amount: 4 }
])

// without result creator
const groups1 = enumerable.groupBy((element) => element.type)

for (const g of groups1) {
  console.log(`Type is ${g[0]} and has ${g[1].length} members.`)
}
// Type is A and has 2 members.
// Type is B and has 1 members.

// with result creator
const groups2 = enumerable.groupBy(
  (element) => element.type,
  (type, elements) => ({
    type,
    amount: elements.sum((item) => item.amount)
  })
)

console.log(groups2.toArray()) // yields [{"type":"A","amount":4},{"type":"B","amount":4}]const enumerable = IEnumerable.from([
  { type: 'A', amount: 1 },
  { type: 'A', amount: 2 },
  { type: 'B', amount: 4 }
])

// without result creator
const groups1 = enumerable.groupBy<string, string>(
  (element) => element.type
)

for (const g of groups1) {
  console.log(`Type is ${g[0]} and has ${g[1].length} members.`)
}
// Type is A and has 2 members.
// Type is B and has 1 members.

// with result creator
const groups2 = enumerable.groupBy(
  (element) => element.type,
  (type, elements) => ({
    type,
    amount: elements!.sum((item) => item.amount)
  })
)

console.log(groups2.toArray()) // yields [{"type":"A","amount":4},{"type":"B","amount":4}]

groupBy with index

const val = IEnumerable.ofRange(1, 10)
  .groupBy(
    (value, index) => index % 2,
    (key, items, index) => [`key ${index % 2}`, items.toArray()]
  )
  .toArray()

// [
//   ["key 0",[1,3,5,7,9]],
//   ["key 1",[2,4,6,8,10]]
// ]const val = IEnumerable.ofRange(1, 10)
  .groupBy(
    (value, index) => index % 2,
    (key, items, index) => [`key ${index % 2}`, items!.toArray()]
  )
  .toArray()

// [
//   ["key 0",[1,3,5,7,9]],
//   ["key 1",[2,4,6,8,10]]
// ]

Using groupBy to create an object

const enumerable = IEnumerable.from([
  { value: 0, key: 'a' },
  { value: 1, key: 'b' },
  { value: 2, key: 'b' },
  { value: 3, key: 'a' }
])

const obj = Object.fromEntries(
  enumerable.groupBy(
    (item) => item.key,
    (key, items) => [key, items.toArray()]
  )
)

// {
//   a: [{value:0, key:a}, {value:3, key:a}],
//   b: [{value:1, key:b}, {value:2, key:b}]
// }const enumerable: IEnumerable<{ value: number; key: string }> =
  IEnumerable.from([
    { value: 0, key: 'a' },
    { value: 1, key: 'b' },
    { value: 2, key: 'b' },
    { value: 3, key: 'a' }
  ])

const obj = Object.fromEntries(
  enumerable.groupBy(
    (item) => item.key,
    (key, items) => [key, items!.toArray()]
  ) as Iterable<[unknown, unknown]>
)

// {
//   a: [{value:0, key:a}, {value:3, key:a}],
//   b: [{value:1, key:b}, {value:2, key:b}]
// }

This implementation differs from the TC39 proposal for array grouping. See the example "Using groupBy to create an object" to mimic the proposal's groupBy behavior.

Overrides

IEnumerable.groupBy

includes

(value: T) : boolean

Determines whether the given value is part of this enumerable.

Parameters

options - Object
A map of options to pass to the method.

value - T: The value to search for.

Returns

↪boolean: true if this enumerable contains the given value, false otherwise.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4])

console.log(enumerable.includes(2)) // true

console.log(enumerable.includes(5)) // false

Overrides

IEnumerable.includes

indexOf

(item: T, fromIndex?: number) : number

The index of the given item in the enumerable.

Parameters

options - Object
A map of options to pass to the method.

item - T: The item to search for.
fromIndex - number

Returns

↪number: The index of the given item in the enumerable. -1 if the item is not in the enumerable.

Overrides

IEnumerable.indexOf

last

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : T

Returns the last element of this enumerable or the last element of this enumerable that matches a given predicate, if specified.

Remarks

The method findLast serves a similar purpose as this method and is more closely modelled on the Array.findLast" method. Consider using that method instead.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A function which returns true if the given element should be returned.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪T: The last element of this enumerable.

Throws

Exception({ name: 'InvalidOperationError' }): If the enumerable is empty.

Examples

const enumerable1 = IEnumerable.from([1, 2, 3, 4])
console.log(enumerable1.last()) // yields 4

// if the enumerable is empty then an exception will be thrown
const enumerable2 = IEnumerable.from([])
console.log(enumerable2.last()) // throws exception

Overrides

IEnumerable.last

lastOrDefault

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : T

Returns the last element of this enumerable, the last element of this enumerable that matches a given predicate, if specified, or null if there is no such element.

Remarks

This method is obsolete. Use the findLast or at methods instead.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A predicate function which returns true if the given element should be returned.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪T: The last element of the enumerable or null.

Examples

const enumerable1 = IEnumerable.from([1, 2, 3, 4])
console.log(enumerable1.lastOrDefault()) // yields 4

// if the enumerable is empty then null will be returned
const enumerable2 = IEnumerable.from([])
console.log(enumerable2.lastOrDefault()) // yields null

Overrides

IEnumerable.lastOrDefault

map

<TResult>(selector: function(T, number, IEnumerable<T>):TResult, thisArg?: Object) : IEnumerable<TResult>

Returns a dynamic IEnumerable<T> of this enumerable using the given selector function which returns a new object for each element of this enumerable.

Remarks

Type Parameters

TResult: The type of the mapped elements.

Parameters

options - Object
A map of options to pass to the method.

selector - function(T, number, IEnumerable<T>):TResult

A function which converts each element into a new element of the type TResult.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : TResult

The selector to use for the IEnumerable<T>.

A function which returns a result of type TResult for each element.

Parameters

element - T: The current element create a result for.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

TResult: A result of type TResult created from the element.

thisArg - Object

The optional value to use as this when executing the selector.

Returns

↪IEnumerable<TResult>: A dynamic enumerable of the results of the provided function.

Examples

const enumerable = IEnumerable.from([1, 2, 3])

const result = enumerable.map((item) => item * 2)

console.log(result.toArray()) // yields [2, 4, 6]

// with index
const result2 = enumerable.map((item, index) => item * index)

console.log(result2.toArray()) // yields [0, 2, 6]

// with index and enumerable
const result3 = enumerable.map(
  (item, index, enumerable) =>
    `Item no ${index} of ${enumerable.size} is ${item}`
)

console.log(result3.toArray())
// ["Item no 0 of 3 is 1","Item no 1 of 3 is 2","Item no 2 of 3 is 3"]const enumerable = IEnumerable.from([1, 2, 3])

const result = enumerable.map((item) => item * 2)

console.log(result.toArray()) // yields [2, 4, 6]

// with index
const result2 = enumerable.map((item, index) => item * index)

console.log(result2.toArray()) // yields [0, 2, 6]

// with index and enumerable
const result3 = enumerable.map(
  (item, index, enumerable) =>
    `Item no ${index} of ${enumerable!.size} is ${item}`
)

console.log(result3.toArray())
// ["Item no 0 of 3 is 1","Item no 1 of 3 is 2","Item no 2 of 3 is 3"]

The returned enumerable is dynamic

const list = List.fromArray([1, 2, 3])

const result = list.map((item) => item * 2)

list.add(4)

// result changed also
console.log(result.toArray()) // yields [2,4,6,8]

Overrides

IEnumerable.map

ofType

<TResult>(resultType: Class) : IEnumerable<TResult>

Converts this untyped enumerable into an enumerable with the given type.

Remarks

The source enumerable may contain elements which are not of the given type. Those elements will not be contained in the returned enumerable.

Type Parameters

TResult

Returns

↪IEnumerable<TResult>: A typed enumerable.

Overrides

IEnumerable.ofType

orderBy

<TKey>(keySelector?: function(T):TKey, comparer?: function(TKey, TKey):number, thisArg?: Object) : IEnumerable<T>

Yields an ordered enumerable of the elements given a key selection function and optional comparison function and creates a ordered view of the enumerable.

Remarks

The sorting will happen each time the enumerable is enumerated.

Type Parameters

TKey

ParametersOptions Overload

options - Object
A map of options to pass to the method.

keySelector - function(T):TKey

The function that determines the key for sorting the elements. If omitted, the element itself is used.

Signature Details

function(element: T) : TKey

A function which creates a key for the given element.

Parameters

element - T: The element to get the key for.

Returns

TKey: The key for the element.

comparer - function(TKey, TKey):number

A function with the signature function(key1, key2):Number which is used for the sort operation to compare the key elements in the enumerable. May be omitted.

Signature Details

function(value1: TKey, value2: TKey) : number

Compares the given values.

Parameters

value1 - TKey: The first value to compare.
value2 - TKey: The second value to compare.

Returns

number: A value less than 0 if value 1 is smaller than value2, 0 if both values are equal, greater than 0 otherwise.

thisArg - Object

Returns

↪IEnumerable<T>: An enumeration of groups of the original enumerable.

Examples

const enumerable = IEnumerable.from([
  { type: 'name-6', rank: 8 },
  { type: 'name-23', rank: 4 },
  { type: 'name-3', rank: 5 }
])

// order by the elements' rank, without a comparer function
const sortedEnumerable1 = enumerable.orderBy((entry) => entry.rank)

console.log(sortedEnumerable1.toArray())
// [{ "type": "name-23", "rank": 4 }, { "type": "name-3", "rank": 5 }, { "type": "name-6", "rank": 8 }]

// order by the elements' type using numeric collation to get a more "natural" order, with a comparer function
const collator = new Intl.Collator(undefined, {
  numeric: true,
  sensitivity: 'base'
})
const sortedEnumerable2 = enumerable.orderBy(
  (entry) => entry.type,
  collator.compare
)

console.log(sortedEnumerable2.toArray())
// [{ "type": "name-3", "rank": 5 }, { "type": "name-6", "rank": 8 },{ "type": "name-23", "rank": 4 }]

Overrides

IEnumerable.orderBy

orderByDescending

<TKey>(keySelector?: function(T):TKey, comparer?: function(TKey, TKey):number, thisArg?: Object) : IEnumerable<T>

Yields an ordered enumerable of the elements given a key selection function and optional comparison function and creates a ordered view of the enumerable where the elements are yielded in descending order.

Remarks

The sorting will happen each time the enumerable is enumerated.

Type Parameters

TKey

ParametersOptions Overload

options - Object
A map of options to pass to the method.

keySelector - function(T):TKey

The function that determines the key for sorting the elements. If omitted, the element itself is used.

Signature Details

function(element: T) : TKey

A function which creates a key for the given element.

Parameters

element - T: The element to get the key for.

Returns

TKey: The key for the element.

comparer - function(TKey, TKey):number

A function with the signature function(key1, key2):Number which is used for the sort operation to compare the key elements in the enumerable. May be omitted.

Signature Details

function(value1: TKey, value2: TKey) : number

Compares the given values.

Parameters

value1 - TKey: The first value to compare.
value2 - TKey: The second value to compare.

Returns

number: A value less than 0 if value 1 is smaller than value2, 0 if both values are equal, greater than 0 otherwise.

thisArg - Object

Returns

↪IEnumerable<T>: An enumeration of groups of the original enumerable.

Examples

const enumerable = IEnumerable.from([
  { type: 'A' },
  { type: 'B' },
  { type: 'C' },
  { type: 'D' }
])

// order by the elements' types, without a comparer function
const sortedEnumerable1 = enumerable.orderByDescending(
  (entry) => entry.type
)

console.log(sortedEnumerable1.toArray())
// [{ "type": "D" }, { "type": "C" }, { "type": "B" }, { "type": "A" }]

Overrides

IEnumerable.orderByDescending

prepend

(items: T…) : IEnumerable<T>

Creates a wrapped enumerable that has on or several elements prepended to it.

Parameters

options - Object
A map of options to pass to the method.

items - T: The item(s) to prepend to the enumeration

Returns

↪IEnumerable<T>: A new live view over the original enumerable that has items prepended to it.

Examples

const enumerable1 = IEnumerable.from([1, 2, 3, 4])
console.log(enumerable1.prepend(0).toArray()) // yields [0,1,2,3,4]

// more than one value can be used too
const enumerable2 = IEnumerable.from([3, 4, 5, 6])
console.log(enumerable2.prepend(1, 2).toArray()) // yields [1,2,3,4,5,6]

Overrides

IEnumerable.prepend

reduce

<TAccumulate>(accumulator: function(TAccumulate, T, number, IEnumerable<T>):TAccumulate, initialValue: TAccumulate) : TAccumulate

Applies the accumulator function to this elements of this enumerable.

Type Parameters

TAccumulate: The type of the accumulated value.

Parameters

options - Object
A map of options to pass to the method.

accumulator - function(TAccumulate, T, number, IEnumerable<T>):TAccumulate

A function which "adds" (accumulates) a value depending on the element and index to the initial value and returns the result.

Signature Details

function(total: TAccumulate, element: T, index: number, source: IEnumerable<T>) : TAccumulate

The accumulator to use for the IEnumerable<T>.

A function which returns a result of type TAccumulate as an accumulation of total and element.

Parameters

total - TAccumulate: The previously returned value of the function.
element - T: The current element to accumulate.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

TAccumulate: A result of type TAccumulate created from the element.

initialValue - TAccumulate

The initial value for the accumulator. Omit/use the reduce overload if you don't want to specify an initial value.

Returns

↪TAccumulate: The result of the accumulation.

Examples

The returned enumerable is dynamic

const enumerable = IEnumerable.from([1, 2, 3, 4, 5])

const result = enumerable.reduce(
  (accumulator, currentValue) => Math.max(accumulator, currentValue),
  0
)

console.log(result) // expected output: 5

Overrides

IEnumerable.reduce(yfiles.collections.Accumulator,TAccumulate)

reduce

(accumulator: function(T, T, number, IEnumerable<T>):T) : T

Applies the accumulator function to this elements of this enumerable.

Parameters

options - Object
A map of options to pass to the method.

accumulator - function(T, T, number, IEnumerable<T>):T

A function which "adds" (accumulates) a value depending on the element and index to the initial value and returns the result.

Signature Details

function(total: T, element: T, index: number, source: IEnumerable<T>) : T

The accumulator to use for the IEnumerable<T>.

A function which returns a result of type TAccumulate as an accumulation of total and element.

Parameters

total - T: The previously returned value of the function.
element - T: The current element to accumulate.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

T: A result of type TAccumulate created from the element.

Returns

↪T: The result of the accumulation.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4, 5])

const result = enumerable.reduce(
  (accumulator, currentValue) => accumulator + currentValue
)

console.log(result) // expected output: 15

Overrides

IEnumerable.reduce(yfiles.collections.Accumulator)

reduceRight

<TAccumulate>(accumulator: function(TAccumulate, T, number, IEnumerable<T>):TAccumulate, initialValue: TAccumulate) : TAccumulate

Applies the accumulator function to this elements of this enumerable in reverse order.

Type Parameters

TAccumulate: The type of the accumulated value.

Parameters

options - Object
A map of options to pass to the method.

accumulator - function(TAccumulate, T, number, IEnumerable<T>):TAccumulate

A function which "adds" (accumulates) a value depending on the element and index to the seed value and returns the result.

Signature Details

function(total: TAccumulate, element: T, index: number, source: IEnumerable<T>) : TAccumulate

The accumulator to use for the IEnumerable<T>.

A function which returns a result of type TAccumulate as an accumulation of total and element.

Parameters

total - TAccumulate: The previously returned value of the function.
element - T: The current element to accumulate.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

TAccumulate: A result of type TAccumulate created from the element.

initialValue - TAccumulate

The initial value for the accumulator. Omit/use the reduceRight overload if you don't want to specify an initial value.

Returns

↪TAccumulate: The final value of the accumulation.

Examples

The returned enumerable is dynamic

const enumerable = IEnumerable.from(['a', 'b', 'c', 'd'])

const result = enumerable.reduceRight(
  (accumulator, currentValue) => currentValue + accumulator,
  '.'
)

console.log(result) // yields 'abcd.'

Overrides

IEnumerable.reduceRight(yfiles.collections.Accumulator,TAccumulate)

reduceRight

(accumulator: function(T, T, number, IEnumerable<T>):T) : T

Applies the accumulator function to this elements of this enumerable in reverse order.

Parameters

options - Object
A map of options to pass to the method.

accumulator - function(T, T, number, IEnumerable<T>):T

A function which "adds" (accumulates) a value depending on the element and index to the seed value and returns the result.

Signature Details

function(total: T, element: T, index: number, source: IEnumerable<T>) : T

The accumulator to use for the IEnumerable<T>.

A function which returns a result of type TAccumulate as an accumulation of total and element.

Parameters

total - T: The previously returned value of the function.
element - T: The current element to accumulate.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

T: A result of type TAccumulate created from the element.

Returns

↪T: The result of the accumulation.

Examples

const enumerable = IEnumerable.from([
  [0, 1],
  [2, 3],
  [4, 5]
])

const result = enumerable.reduceRight((accumulator, currentValue) =>
  accumulator.concat(currentValue)
)

console.log(result) // yields [4,5,2,3,0,1]

Overrides

IEnumerable.reduceRight(yfiles.collections.Accumulator)

skip

(amount: number) : IEnumerable<T>

Creates a wrapped view of an enumerable which skips the given amount of elements.

Parameters

options - Object
A map of options to pass to the method.

amount - number: The number of elements to skip at the beginning.

Returns

↪IEnumerable<T>: A new live view over the original enumerable that skips amount elements.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4, 5, 6, 7])

const result = enumerable.skip(3)

console.log(result.toArray()) // yields [4,5,6,7]

Overrides

IEnumerable.skip

skipWhile

(predicate: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : IEnumerable<T>

Creates a wrapped view of an enumerable which skips a number of elements at the beginning while the given predicate yields true.

Remarks

While the predicate yields true for the elements of the original enumerable, the elements are skipped. The new enumeration will start with the first element for which the predicate yields false. All subsequent elements will be yielded.

Parameters

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

The predicate function that determines what elements should be skipped. While the predicate yields true for the provided item, the element will not be yielded.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for thisin the predicate function.

Returns

↪IEnumerable<T>: A new live view over the original enumerable that discards elements at the beginnging of the original enumeration while the predicate yields true.

Examples

const enumerable = IEnumerable.from([
  'a',
  'b',
  'c',
  'd',
  'a',
  'b',
  'c',
  'd'
])

const result = enumerable.skipWhile(
  (element) => element.charCodeAt(0) < 'c'.charCodeAt(0)
)

console.log(result.toArray()) // yields ["c", "d", "a", "b", "c", "d"]

Overrides

IEnumerable.skipWhile

some

(predicate?: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : boolean

Determines whether this enumerable contains any elements matching the given predicate.

ParametersOptions Overload

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A function which returns true if the element matches a condition.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for this in the function.

Returns

↪boolean: Whether this enumerable contains any elements matching the given predicate.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4, 5, 6, 7])

const result = enumerable.some((item) => item % 2 === 0)

console.log(result) // true

Overrides

IEnumerable.some

sum

(selector: function(T, number, IEnumerable<T>):number, thisArg?: Object) : number

Calculates the sum of the elements of this enumerable.

Parameters

options - Object
A map of options to pass to the method.

selector - function(T, number, IEnumerable<T>):number

A function which returns a numeric value for the given element.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : number

The selector to use for the IEnumerable<T>.

A function which returns a result of type TResult for each element.

Parameters

element - T: The current element create a result for.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

number: A result of type TResult created from the element.

thisArg - Object

The optional object to use for this in the function.

Returns

↪number: The sum of the elements of the enumerable.

Examples

const enumerable = IEnumerable.from([
  { type: 'A', amount: 3 },
  { type: 'B', amount: 2 },
  { type: 'C', amount: 2 },
  { type: 'D', amount: 5 }
])

const result = enumerable.sum((element) => element.amount)

console.log(result) // yields 12

Overrides

IEnumerable.sum

take

(count: number) : IEnumerable<T>

Creates a dynamic view of this enumerable with the given number of elements taken from the start or end of this enumerable.

Parameters

options - Object
A map of options to pass to the method.

count - number: The number of elements in the created enumerable. If the number is positive, the elements are taken from the beginning, otherwise, the elements are taken from the end.

Returns

↪IEnumerable<T>: A dynamic iew of this enumerable with the given number of elements.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4, 5, 6, 7])

// positive parameter means taking elements from the beginning of the enumerable
console.log(enumerable.take(2).toArray()) // yields [1,2]

// negative parameter means taking elements from the end of the enumerable
console.log(enumerable.take(-2).toArray()) // yields [6,7]

Overrides

IEnumerable.take

takeWhile

(predicate: function(T, number, IEnumerable<T>):boolean, thisArg?: Object) : IEnumerable<T>

Returns a dynamic IEnumerable<T> that contains the elements from this enumerable as long as the given predicate is true.

Remarks

Parameters

options - Object
A map of options to pass to the method.

predicate - function(T, number, IEnumerable<T>):boolean

A function which returns true as long as the elements should be added to the returned enumerable.

Signature Details

function(element: T, index: number, source: IEnumerable<T>) : boolean

The predicate to use for IEnumerable<T>.

Parameters

element - T: The current element to test.
index - number: The element's index in the
source - IEnumerable<T>: The enumerable this function is called upon.

Returns

boolean: true if the item matches the condition.

thisArg - Object

The optional object to use for thisin the function.

Returns

↪IEnumerable<T>: A dynamic enumerable that is a subset of the original enumerable.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 30, 4, 5])

const result = enumerable.takeWhile((item) => item < 5)

console.log(result.toArray()) // yields [1,2,3]

Overrides

IEnumerable.takeWhile

toArray

() : T

Creates an array with the elements of this enumerable.

Returns

↪T[]: An array with the elements of this enumerable.

Overrides

IEnumerable.toArray

toList

() : List<T>

Creates a List<T> with the values of this enumerable.

Returns

↪List<T>: A List<T> of the elements of this enumerable.

Overrides

IEnumerable.toList

toReversed

() : IEnumerable<T>

Returns an dynamic enumerable which contains the elements of this enumerable in reverse order.

Remarks

Returns

↪IEnumerable<T>: A dynamic enumerable which contains the elements of the original enumerable in reverse order.

Examples

const enumerable = IEnumerable.from([1, 2, 3, 4, 5])

const result = enumerable.toReversed()

console.log(result.toArray()) // yields [5,4,3,2,1]

The returned enumerable is dynamic

const list = List.fromArray([1, 2, 3, 4, 5])

const result = list.toReversed()

list.add(0)

// result changed also
console.log(result.toArray()) // yields [0,5,4,3,2,1]

Overrides

IEnumerable.toReversed

ListEnumerable<T>

Remarks

Type Parameters

Type Details

Constructors

ListEnumerable

ListEnumerable

Remarks

Parameters

Properties

backingEnumerable

size

Overrides

Methods

append

Remarks

Parameters

Returns

Examples

See Also

Overrides

at

Parameters

Returns

Examples

Overrides

concat

Remarks

Parameters

Returns

Examples

See Also

Overrides

distinct

Remarks

ParametersOptions Overload

Signature Details

Parameters

Returns

Returns

Examples

See Also

Overrides

elementAt

Remarks

Parameters

Returns

Throws

Examples

See Also

Overrides

every

Parameters

Signature Details

Parameters

Returns

Returns

Throws

Examples

Overrides

filter

Remarks

Parameters

Signature Details

Parameters

Returns

Returns

Examples

Overrides

find

ParametersOptions Overload

Signature Details

Parameters

Returns

Returns

Examples

Overrides

findIndex

Parameters

Signature Details