abp/docs/en/UI/Common/Utils/Linked-List.md

Linked List (Doubly)

The core module provides a useful data structure known as a doubly linked list. Briefly, a doubly linked list is a series of records (a.k.a. nodes) which has information on the previous node, the next node, and its own value (or data).

Getting Started

To create a doubly linked list, all you have to do is to import and create a new instance of it:

import { LinkedList } from '@abp/ng.core';

const list = new LinkedList();

The constructor does not get any parameters.

Usage

How to Add New Nodes

There are several methods to create new nodes in a linked list and all of them are separately available as well as revealed by add and addMany methods.

addHead(value: T): ListNode<T>

Adds a node with given value as the first node in list:

list.addHead('a');

// "a"

list.addHead('b');

// "b" <-> "a"

list.addHead('c');

// "c" <-> "b" <-> "a"

addManyHead(values: T[]): ListNode<T>[]

Adds multiple nodes with given values as the first nodes in list:

list.addManyHead(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

list.addManyHead(['x', 'y', 'z']);

// "x" <-> "y" <-> "z" <-> "a" <-> "b" <-> "c"

addTail(value: T): ListNode<T>

Adds a node with given value as the last node in list:

list.addTail('a');

// "a"

list.addTail('b');

// "a" <-> "b"

list.addTail('c');

// "a" <-> "b" <-> "c"

addManyTail(values: T[]): ListNode<T>[]

Adds multiple nodes with given values as the last nodes in list:

list.addManyTail(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

list.addManyTail(['x', 'y', 'z']);

// "a" <-> "b" <-> "c" <-> "x" <-> "y" <-> "z"

addAfter(value: T, previousValue: T, compareFn = compare): ListNode<T>

Adds a node with given value after the first node that has the previous value:

list.addTail('a');
list.addTail('b');
list.addTail('b');
list.addTail('c');

// "a" <-> "b" <-> "b" <-> "c"

list.addAfter('x', 'b');

// "a" <-> "b" <-> "x" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addTail({ x: 1 });
list.addTail({ x: 2 });
list.addTail({ x: 3 });

// {"x":1} <-> {"x":2} <-> {"x":3}

list.addAfter(
  { x: 0 },
  2,
  (value, searchedValue) => value.x === searchedValue
);

// {"x":1} <-> {"x":2} <-> {"x":0} <-> {"x":3}

The default compare function checks deep equality, so you will rarely need to pass that parameter.

addManyAfter(values: T[], previousValue: T, compareFn = compare): ListNode<T>[]

Adds multiple nodes with given values after the first node that has the previous value:

list.addManyTail(['a', 'b', 'b', 'c']);

// "a" <-> "b" <-> "b" <-> "c"

list.addManyAfter(['x', 'y'], 'b');

// "a" <-> "b" <-> "x" <-> "y" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addManyTail([{ x: 1 },{ x: 2 },{ x: 3 }]);

// {"x":1} <-> {"x":2} <-> {"x":3}

list.addManyAfter(
  [{ x: 4 }, { x: 5 }],
  2,
  (value, searchedValue) => value.x === searchedValue
);

// {"x":1} <-> {"x":2} <-> {"x":4} <-> {"x":5} <-> {"x":3}

The default compare function checks deep equality, so you will rarely need to pass that parameter.

addBefore(value: T, nextValue: T, compareFn = compare): ListNode<T>

Adds a node with given value before the first node that has the next value:

list.addTail('a');
list.addTail('b');
list.addTail('b');
list.addTail('c');

// "a" <-> "b" <-> "b" <-> "c"

list.addBefore('x', 'b');

// "a" <-> "x" <-> "b" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addTail({ x: 1 });
list.addTail({ x: 2 });
list.addTail({ x: 3 });

// {"x":1} <-> {"x":2} <-> {"x":3}

list.addBefore(
  { x: 0 },
  2,
  (value, searchedValue) => value.x === searchedValue
);

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":3}

The default compare function checks deep equality, so you will rarely need to pass that parameter.

addManyBefore(values: T[], nextValue: T, compareFn = compare): ListNode<T>[]

Adds multiple nodes with given values before the first node that has the next value:

list.addManyTail(['a', 'b', 'b', 'c']);

// "a" <-> "b" <-> "b" <-> "c"

list.addManyBefore(['x', 'y'], 'b');

// "a" <-> "x" <-> "y" <-> "b" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addManyTail([{ x: 1 },{ x: 2 },{ x: 3 }]);

// {"x":1} <-> {"x":2} <-> {"x":3}

list.addManyBefore(
  [{ x: 4 }, { x: 5 }],
  2,
  (value, searchedValue) => value.x === searchedValue
);

// {"x":1} <-> {"x":4} <-> {"x":5} <-> {"x":2} <-> {"x":3}

The default compare function checks deep equality, so you will rarely need to pass that parameter.

addByIndex(value: T, position: number): ListNode<T>

Adds a node with given value at the specified position in the list:

list.addTail('a');
list.addTail('b');
list.addTail('c');

// "a" <-> "b" <-> "c"

list.addByIndex('x', 2);

// "a" <-> "b" <-> "x" <-> "c"

It works with negative index too:

list.addTail('a');
list.addTail('b');
list.addTail('c');

// "a" <-> "b" <-> "c"

list.addByIndex('x', -1);

// "a" <-> "b" <-> "x" <-> "c"

addManyByIndex(values: T[], position: number): ListNode<T>[]

Adds multiple nodes with given values at the specified position in the list:

list.addManyTail(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

list.addManyByIndex(['x', 'y'], 2);

// "a" <-> "b" <-> "x" <-> "y" <-> "c"

It works with negative index too:

list.addManyTail(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

list.addManyByIndex(['x', 'y'], -1);

// "a" <-> "b" <-> "x" <-> "y" <-> "c"

add(value: T).head(): ListNode<T>

Adds a node with given value as the first node in list:

list.add('a').head();

// "a"

list.add('b').head();

// "b" <-> "a"

list.add('c').head();

// "c" <-> "b" <-> "a"

This is an alternative API for addHead.

add(value: T).tail(): ListNode<T>

Adds a node with given value as the last node in list:

list.add('a').tail();

// "a"

list.add('b').tail();

// "a" <-> "b"

list.add('c').tail();

// "a" <-> "b" <-> "c"

This is an alternative API for addTail.

add(value: T).after(previousValue: T, compareFn = compare): ListNode<T>

Adds a node with given value after the first node that has the previous value:

list.add('a').tail();
list.add('b').tail();
list.add('b').tail();
list.add('c').tail();

// "a" <-> "b" <-> "b" <-> "c"

list.add('x').after('b');

// "a" <-> "b" <-> "x" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.add({ x: 1 }).tail();
list.add({ x: 2 }).tail();
list.add({ x: 3 }).tail();

// {"x":1} <-> {"x":2} <-> {"x":3}

list
  .add({ x: 0 })
  .after(2, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":2} <-> {"x":0} <-> {"x":3}

This is an alternative API for addAfter.

The default compare function checks deep equality, so you will rarely need to pass that parameter.

add(value: T).before(nextValue: T, compareFn = compare): ListNode<T>

Adds a node with given value before the first node that has the next value:

list.add('a').tail();
list.add('b').tail();
list.add('b').tail();
list.add('c').tail();

// "a" <-> "b" <-> "b" <-> "c"

list.add('x').before('b');

// "a" <-> "x" <-> "b" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.add({ x: 1 }).tail();
list.add({ x: 2 }).tail();
list.add({ x: 3 }).tail();

// {"x":1} <-> {"x":2} <-> {"x":3}

list
  .add({ x: 0 })
  .before(2, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":3}

This is an alternative API for addBefore.

The default compare function checks deep equality, so you will rarely need to pass that parameter.

add(value: T).byIndex(position: number): ListNode<T>

Adds a node with given value at the specified position in the list:

list.add('a').tail();
list.add('b').tail();
list.add('c').tail();

// "a" <-> "b" <-> "c"

list.add('x').byIndex(2);

// "a" <-> "b" <-> "x" <-> "c"

It works with negative index too:

list.add('a').tail();
list.add('b').tail();
list.add('c').tail();

// "a" <-> "b" <-> "c"

list.add('x').byIndex(-1);

// "a" <-> "b" <-> "x" <-> "c"

This is an alternative API for addByIndex.

addMany(values: T[]).head(): ListNode<T>[]

Adds multiple nodes with given values as the first nodes in list:

list.addMany(['a', 'b', 'c']).head();

// "a" <-> "b" <-> "c"

list.addMany(['x', 'y', 'z']).head();

// "x" <-> "y" <-> "z" <-> "a" <-> "b" <-> "c"

This is an alternative API for addManyHead.

addMany(values: T[]).tail(): ListNode<T>[]

Adds multiple nodes with given values as the last nodes in list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.addMany(['x', 'y', 'z']).tail();

// "a" <-> "b" <-> "c" <-> "x" <-> "y" <-> "z"

This is an alternative API for addManyTail.

addMany(values: T[]).after(previousValue: T, compareFn = compare): ListNode<T>[]

Adds multiple nodes with given values after the first node that has the previous value:

list.addMany(['a', 'b', 'b', 'c']).tail();

// "a" <-> "b" <-> "b" <-> "c"

list.addMany(['x', 'y']).after('b');

// "a" <-> "b" <-> "x" <-> "y" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addMany([{ x: 1 }, { x: 2 }, { x: 3 }]).tail();

// {"x":1} <-> {"x":2} <-> {"x":3}

list
  .addMany([{ x: 4 }, { x: 5 }])
  .after(2, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":2} <-> {"x":4} <-> {"x":5} <-> {"x":3}

This is an alternative API for addManyAfter.

The default compare function checks deep equality, so you will rarely need to pass that parameter.

addMany(values: T[]).before(nextValue: T, compareFn = compare): ListNode<T>[]

Adds multiple nodes with given values before the first node that has the next value:

list.addMany(['a', 'b', 'b', 'c']).tail();

// "a" <-> "b" <-> "b" <-> "c"

list.addMany(['x', 'y']).before('b');

// "a" <-> "x" <-> "y" <-> "b" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addMany([{ x: 1 }, { x: 2 }, { x: 3 }]).tail();

// {"x":1} <-> {"x":2} <-> {"x":3}

list
  .addMany([{ x: 4 }, { x: 5 }])
  .before(2, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":4} <-> {"x":5} <-> {"x":2} <-> {"x":3}

This is an alternative API for addManyBefore.

The default compare function checks deep equality, so you will rarely need to pass that parameter.

addMany(values: T[]).byIndex(position: number): ListNode<T>[]

Adds multiple nodes with given values at the specified position in the list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.addMany(['x', 'y']).byIndex(2);

// "a" <-> "b" <-> "x" <-> "y" <-> "c"

It works with negative index too:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.addMany(['x', 'y']).byIndex(-1);

// "a" <-> "b" <-> "x" <-> "y" <-> "c"

This is an alternative API for addManyByIndex.

How to Remove Nodes

There are a few methods to remove nodes from a linked list and all of them are separately available as well as revealed from a drop method.

dropHead(): ListNode<T> | undefined

Removes the first node from the list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropHead();

// "b" <-> "c"

dropManyHead(count: number): ListNode<T>[]

Removes the first nodes from the list based on given count:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropManyHead(2);

// "c"

dropTail(): ListNode<T> | undefined

Removes the last node from the list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropTail();

// "a" <-> "b"

dropManyTail(count: number): ListNode<T>[]

Removes the last nodes from the list based on given count:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropManyTail(2);

// "a"

dropByIndex(position: number): ListNode<T> | undefined

Removes the node with the specified position from the list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropByIndex(1);

// "a" <-> "c"

It works with negative index too:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropByIndex(-2);

// "a" <-> "c"

dropManyByIndex(count: number, position: number): ListNode<T>[]

Removes the nodes starting from the specified position from the list based on given count:

list.addMany(['a', 'b', 'c', 'd']).tail();

// "a" <-> "b" <-> "c" <-> "d

list.dropManyByIndex(2, 1);

// "a" <-> "d"

It works with negative index too:

list.addMany(['a', 'b', 'c', 'd']).tail();

// "a" <-> "b" <-> "c" <-> "d

list.dropManyByIndex(2, -2);

// "a" <-> "d"

dropByValue(value: T, compareFn = compare): ListNode<T> | undefined

Removes the first node with given value from the list:

list.addMany(['a', 'x', 'b', 'x', 'c']).tail();

// "a" <-> "x" <-> "b" <-> "x" <-> "c"

list.dropByValue('x');

// "a" <-> "b" <-> "x" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addMany([{ x: 1 }, { x: 0 }, { x: 2 }, { x: 0 }, { x: 3 }]).tail();

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":0} <-> {"x":3}

list.dropByValue(0, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":2} <-> {"x":0} <-> {"x":3}

The default compare function checks deep equality, so you will rarely need to pass that parameter.

dropByValueAll(value: T, compareFn = compare): ListNode<T>[]

Removes all nodes with given value from the list:

list.addMany(['a', 'x', 'b', 'x', 'c']).tail();

// "a" <-> "x" <-> "b" <-> "x" <-> "c"

list.dropByValueAll('x');

// "a" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addMany([{ x: 1 }, { x: 0 }, { x: 2 }, { x: 0 }, { x: 3 }]).tail();

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":0} <-> {"x":3}

list.dropByValue(0, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":2} <-> {"x":3}

The default compare function checks deep equality, so you will rarely need to pass that parameter.

drop().head(): ListNode<T> | undefined

Removes the first node in list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.drop().head();

// "b" <-> "c"

This is an alternative API for dropHead.

drop().tail(): ListNode<T> | undefined

Removes the last node in list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.drop().tail();

// "a" <-> "b"

This is an alternative API for dropTail.

drop().byIndex(position: number): ListNode<T> | undefined

Removes the node with the specified position from the list:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.drop().byIndex(1);

// "a" <-> "c"

It works with negative index too:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.drop().byIndex(-2);

// "a" <-> "c"

This is an alternative API for dropByIndex.

drop().byValue(value: T, compareFn = compare): ListNode<T> | undefined

Removes the first node with given value from the list:

list.addMany(['a', 'x', 'b', 'x', 'c']).tail();

// "a" <-> "x" <-> "b" <-> "x" <-> "c"

list.drop().byValue('x');

// "a" <-> "b" <-> "x" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addMany([{ x: 1 }, { x: 0 }, { x: 2 }, { x: 0 }, { x: 3 }]).tail();

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":0} <-> {"x":3}

list
  .drop()
  .byValue(0, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":2} <-> {"x":0} <-> {"x":3}

This is an alternative API for dropByValue.

The default compare function checks deep equality, so you will rarely need to pass that parameter.

drop().byValueAll(value: T, compareFn = compare): ListNode<T>[]

Removes all nodes with given value from the list:

list.addMany(['a', 'x', 'b', 'x', 'c']).tail();

// "a" <-> "x" <-> "b" <-> "x" <-> "c"

list.drop().byValueAll('x');

// "a" <-> "b" <-> "c"

You may pass a custom compare function to detect the searched value:

list.addMany([{ x: 1 }, { x: 0 }, { x: 2 }, { x: 0 }, { x: 3 }]).tail();

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":0} <-> {"x":3}

list
  .drop()
  .byValueAll(0, (value, searchedValue) => value.x === searchedValue);

// {"x":1} <-> {"x":2} <-> {"x":3}

This is an alternative API for dropByValueAll.

The default compare function checks deep equality, so you will rarely need to pass that parameter.

dropMany(count: number).head(): ListNode<T>[]

Removes the first nodes from the list based on given count:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropMany(2).head();

// "c"

This is an alternative API for dropManyHead.

dropMany(count: number).tail(): ListNode<T>[]

Removes the last nodes from the list based on given count:

list.addMany(['a', 'b', 'c']).tail();

// "a" <-> "b" <-> "c"

list.dropMany(2).tail();

// "a"

This is an alternative API for dropManyTail.

dropMany(count: number).byIndex(position: number): ListNode<T>[]

Removes the nodes starting from the specified position from the list based on given count:

list.addMany(['a', 'b', 'c', 'd']).tail();

// "a" <-> "b" <-> "c" <-> "d

list.dropMany(2).byIndex(1);

// "a" <-> "d"

It works with negative index too:

list.addMany(['a', 'b', 'c', 'd']).tail();

// "a" <-> "b" <-> "c" <-> "d

list.dropMany(2).byIndex(-2);

// "a" <-> "d"

This is an alternative API for dropManyByIndex.

How to Find Nodes

There are a few methods to find specific nodes in a linked list.

find(predicate: ListIteratorFunction<T>): ListNode<T> | undefined

Finds the first node from the list that matches the given predicate:

list.addTailMany(['a', 'b', 'b', 'c']);

// "a" <-> "b" <-> "b" <-> "c"

const found = list.find(node => node.value === 'b');

/*
found.value === "b"
found.previous.value === "a"
found.next.value === "b"
*/

findIndex(predicate: ListIteratorFunction<T>): number

Finds the position of the first node from the list that matches the given predicate:

list.addTailMany(['a', 'b', 'b', 'c']);

// "a" <-> "b" <-> "b" <-> "c"

const i0 = list.findIndex(node => node.next && node.next.value === 'b');
const i1 = list.findIndex(node => node.value === 'b');
const i2 = list.findIndex(node => node.previous && node.previous.value === 'b');
const i3 = list.findIndex(node => node.value === 'x');

/*
i0 === 0
i1 === 1
i2 === 2
i3 === -1
*/

get(position: number): ListNode<T> | undefined

Finds and returns the node with specific position in the list:

list.addTailMany(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

const found = list.get(1);

/*
found.value === "b"
found.previous.value === "a"
found.next.value === "c"
*/

indexOf(value: T, compareFn = compare): number

Finds the position of the first node from the list that has the given value:

list.addTailMany(['a', 'b', 'b', 'c']);

// "a" <-> "b" <-> "b" <-> "c"

const i0 = list.indexOf('a');
const i1 = list.indexOf('b');
const i2 = list.indexOf('c');
const i3 = list.indexOf('x');

/*
i0 === 0
i1 === 1
i2 === 3
i3 === -1
*/

You may pass a custom compare function to detect the searched value:

list.addTailMany([{ x: 1 }, { x: 0 }, { x: 2 }, { x: 0 }, { x: 3 }]);

// {"x":1} <-> {"x":0} <-> {"x":2} <-> {"x":0} <-> {"x":3}

const i0 = indexOf(1, (value, searchedValue) => value.x === searchedValue);
const i1 = indexOf(2, (value, searchedValue) => value.x === searchedValue);
const i2 = indexOf(3, (value, searchedValue) => value.x === searchedValue);
const i3 = indexOf(0, (value, searchedValue) => value.x === searchedValue);
const i4 = indexOf(4, (value, searchedValue) => value.x === searchedValue);

/*
i0 === 0
i1 === 2
i2 === 4
i3 === 1
i4 === -1
*/

The default compare function checks deep equality, so you will rarely need to pass that parameter.

How to Check All Nodes

There are a few ways to iterate over or display a linked list.

forEach(callback: ListIteratorFunction<T>): void

Runs a callback function on all nodes in a linked list from head to tail:

list.addTailMany(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

list.forEach((node, index) => console.log(node.value + index));

// 'a0'
// 'b1'
// 'c2'

*[Symbol.iterator]

A linked list is iterable. In other words, you may use methods like for...of on it.

list.addTailMany(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

for(const node of list) {
  console.log(node.value);
}

// 'a'
// 'b'
// 'c'

toArray(): T[]

Converts a linked list to an array of values:

list.addTailMany(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

const arr = list.toArray();

/*
arr === ['a', 'b', 'c']
*/

toNodeArray(): T[]

Converts a linked list to an array of nodes:

list.addTailMany(['a', 'b', 'c']);

// "a" <-> "b" <-> "c"

const arr = list.toNodeArray();

/*
arr[0].value === 'a'
arr[1].value === 'a'
arr[2].value === 'a'
*/

toString(): string

Converts a linked list to a string representation of nodes and their relations:

list.addTailMany(['a', 2, 'c', { k: 4, v: 'd' }]);

// "a" <-> 2 <-> "c" <-> {"k":4,"v":"d"}

const str = list.toString();

/*
str === '"a" <-> 2 <-> "c" <-> {"k":4,"v":"d"}'
*/

You may pass a custom mapper function to map values before stringifying them:

list.addMany([{ x: 1 }, { x: 2 }, { x: 3 }, { x: 4 }, { x: 5 }]).tail();

// {"x":1} <-> {"x":2} <-> {"x":3} <-> {"x":4} <-> {"x":5}

const str = list.toString(value => value.x);

/*
str === '1 <-> 2 <-> 3 <-> 4 <-> 5'
*/