Js array deduplication method summary, js array Summary

Js array deduplication method summary, js array Summary

Three methods

Use indexOf to determine the new array

Similar indexOf is actually used in underscore. js.

// Input the Array function unique1 (arr) {var tmpArr = []; for (var I = 0; I <arr. length; I ++) {// if the I of the current array has been saved in a temporary array, skip this step. // otherwise, push the current item to the temporary array if (tmpArr. indexOf (arr [I]) =-1) {tmpArr. push (arr [I]);} return tmpArr ;}

Use indexOf to determine the old Array

Function unique2 (arr) {var tmpArr = []; // result array for (var I = 0; I <arr. length; I ++) {// if the position where the I entry of the current array appears for the first time in the current array is not I, // It indicates that the I entry is repeated, ignore. Otherwise, the stored result array if (arr. indexOf (arr [I]) = I) {tmpArr. push (arr [I]) ;}} return tmpArr ;}

Search by hash

The implementation of JS objects is the feature of hash tables.

Function unique3 (arr) {var tmpArr = [], hash = {}; // hash is the hash table for (var I = 0; I <arr. length; I ++) {if (! Hash [arr [I]) {// If the hash table does not have the current item hash [arr [I] = true; // save it to the hash table tmpArr. push (arr [I]); // save to a temporary array} return tmpArr ;}

Array Extension

Array. prototype. unique1 = function () {var tmpArr = []; for (var I = 0; I <this. length; I ++) {if (tmpArr. indexOf (this [I]) =-1) {tmpArr. push (this [I]);} return tmpArr;} Array. prototype. unique2 = function () {var tmpArr = []; // result array for (var I = 0; I <this. length; I ++) {if (this. indexOf (this [I]) = I) {tmpArr. push (this [I]);} return tmpArr;} Array. prototype. unique3 = function () {var tmpArr = [] , Hash = {}; for (var I = 0; I <this. length; I ++) {if (! Hash [this [I]) {hash [this [I] = true; tmpArr. push (this [I]) ;}} return tmpArr ;}

Use Set

Set and Map are new data structures in ES6.
Set can directly store a Set of keys that are not repeated. This key can also be an object or a string.
Create a set

var s = new Set([1, 2, 3,]);s; // Set {1, 2, 3}

Add Element

>>> S. add (4) >>> s {1, 2, 3, 4 }>>> s. add (4) >>> s {1, 2, 3, 4} // duplicate elements are not added

Delete Element

s; // Set {1, 2, 3, 4}s.delete(3);s; // Set {1, 2, 4}

Traversal Element

Map and Set cannot use subscript
The ES6 standard introduces the new iterable type. Array, Map, and Set all belong to the iterable type.

Var s = new Set (['A', 'B', 'C']); for (var x of s) {// traverse Set alert (x );}

Or you can directly use the iterable built-in forEach method.
The forEach method is introduced in the ES5.1 standard.

var s = new Set(['A', 'B', 'C']);s.forEach(function (element, set) {  alert(element);});

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