Array to heavy, is generally in the interview will encounter, is generally required to handwritten array to heavy method of code. If you are asked, what are the methods of array de-duplication? If you can answer 10 of these questions, there’s a good chance you’ll impress your interviewer. Array deduplicating encountered in real projects is generally handled by the background, rarely let the front end deal with array deduplicating. Although the probability of daily projects is relatively low, but still need to know, in case the interview may be asked back.
Note: I am writing in a hurry, and I have been a little busy these days, so I haven’t checked it carefully. However, there is no problem in my thinking, and some small details may be wrong.
A method to remove the weight of an array
ES6 Set (most commonly used in ES6)
Function unique (arr) {return Array. The from (new Set (arr)]} var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined,undefined, null,null, NaN, NaN,'NaN', 0, 0, 'a', 'a',{},{}]; console.log(unique(arr)) //[1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {}, {}]Copy the codeRegardless of compatibility, this method of de-duplication has the least code. This method also does not remove the empty ‘{}’ object; later higher-order methods add methods to remove the duplicate ‘{}’ object.
2, use for to nest for, and then splice (ES5 most commonly used)
function unique(arr){ for(var i=0; i<arr.length; i++){ for(var j=i+1; j<arr.length; J ++){if(arr[I]==arr[j]){// if(arr[I]==arr[j]); j--; } } } return arr; } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; Console. log(unique(arr)) //[1, "true", 15, false, undefined, NaN, NaN, "NaN", "a", {...}, {...}] //NaN and {} are nullCopy the codeDouble loop, outer loop elements, inner loop when comparing values. If the values are the same, delete this value. For a quick look at more commonly used ES6 grammars, see my previous post, “Learning ES6 Notes — ES6 Grammars used in your Work.”
3. Use indexOf to remove weight
function unique(arr) { if (! Array.isArray(arr)) { console.log('type error! ') return } var array = []; for (var i = 0; i < arr.length; i++) { if (array .indexOf(arr[i]) === -1) { array .push(arr[i]) } } return array; } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; The console. The log (unique (arr)) / / [1, "true", true, 15, false, undefined, null, NaN, NaN, "NaN," 0, "a", {...}, {... }] //NaN, {} are not deduplicatedCopy the codeCreate an empty result array, loop through the original array, check whether the result array has the current element, skip if they have the same value, push into the array if they do not.
Sort ()
function unique(arr) { if (! Array.isArray(arr)) { console.log('type error! ') return; } arr = arr.sort() var arrry= [arr[0]]; for (var i = 1; i < arr.length; i++) { if (arr[i] ! == arr[i-1]) { arrry.push(arr[i]); } } return arrry; } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; The console. The log (unique (arr)) / / [0, 1, 15, "NaN," NaN, NaN, {...}, {... }, "a", false, null, true, "true", undefined] //NaN, {} is not de-weightedCopy the codeUse sort() sorting method, and then traverse and compare adjacent elements according to the sorted result.
5, the use of object attributes can not be the same characteristics for deduplication (this array deduplication method has problems, not recommended, need to be improved)
function unique(arr) { if (! Array.isArray(arr)) { console.log('type error! ') return } var arrry= []; var obj = {}; for (var i = 0; i < arr.length; i++) { if (! obj[arr[i]]) { arrry.push(arr[i]) obj[arr[i]] = 1 } else { obj[arr[i]]++ } } return arrry; } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; Console. log(unique(arr)) //[1, "true", 15, false, undefined, null, NaN, 0, "a", {...}Copy the codeVi. Use includes
function unique(arr) { if (! Array.isArray(arr)) { console.log('type error! ') return } var array =[]; for(var i = 0; i < arr.length; i++) { if( ! Array.push (arr[I]); array.push(arr[I]); }} return array} var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,'NaN', 0, 0, 'a', 'a',{},{}]; The console. The log (unique (arr)) / / [1, "true", true, 15, false, undefined, null, NaN, "NaN," 0, "a", {...}, {...}] / / {} not to heavyCopy the codeUse hasOwnProperty
function unique(arr) { var obj = {}; return arr.filter(function(item, index, arr){ return obj.hasOwnProperty(typeof item + item) ? false : (obj [typeof item + item] = true)})} var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined. null,null, NaN, NaN,'NaN', 0, 0, 'a', 'a',{},{}]; Console. log(unique(arr)) //[1, "true", true, 15, false, undefined, null, NaN, "NaN", 0, "a", {...}Copy the codeUse hasOwnProperty to determine whether an object property exists
8. Use filter
Arr. Filter (function(item, index, arr) {return arr. Filter (function(item, index, arr) {return arr. Return arr.indexof (item, 0) === index; }); } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; The console. The log (unique (arr)) / / [1, "true", true, 15, false, undefined, null, "NaN," 0, "a", {...}, {...}]Copy the codeUse recursion to duplicate
function unique(arr) {
var array= arr;
var len = array.length;
array.sort(function(a,b){ //排序后更加方便去重
return a - b;
})
function loop(index){
if(index >= 1){
if(array[index] === array[index-1]){
array.splice(index,1);
}
loop(index - 1); //递归loop，然后数组去重
}
}
loop(len-1);
return array;
}
var arr = [1,1,'true','true',true,true,15,15,false,false, undefined,undefined, null,null, NaN, NaN,'NaN', 0, 0, 'a', 'a',{},{}];
console.log(unique(arr))
//[1, "a", "true", true, 15, false, 1, {…}, null, NaN, NaN, "NaN", 0, "a", {…}, undefined]
Copy the code10. Use Map data structure to remove weight
function arrayNonRepeatfy(arr) { let map = new Map(); let array = new Array(); For (let I = 0; i < arr.length; I++) {if (map) from the (arr) [I]) {/ / if you have the key value map. The set (arr [I], true); } else { map .set(arr[i], false); Array.push (arr[I]); } } return array ; } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; The console. The log (unique (arr)) / / [1, "a", "true", true, 15, false, 1, {...}, null, NaN, NaN, "NaN," 0, "a", {...}, undefined]Copy the codeCreate an empty Map data structure that iterates through the array to be repealed, storing each element of the array as a key in the Map. Since the Map does not have the same key value, the final result is the result after the deduplication.
11. Use reduce+includes
function unique(arr){ return arr.reduce((prev,cur) => prev.includes(cur) ? prev : [...prev,cur],[]); } var arr = [1, 1, 'true', 'true, true, true, 15, 15, false, false, undefined, undefined, null, null, NaN, NaN,' NaN ', 0, 0, 'a', 'a',{},{}]; console.log(unique(arr)); / / (1, "true", true, 15, false, undefined, null, NaN, "NaN," 0, "a", {...}, {...}]Copy the code12, […new Set(arr)]
[...new Set(arr)] ----Copy the codeForeach +indexOf = foreach+indexOf = foreach