11 ways to remove duplicates from js arrays
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In actual work or interviews, we often encounter the problem of "array deduplication". The following are various methods of array deduplication implemented using js: 1. Compare each element of the array with other elements in turn, find duplicate elements, and delete them
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5,5,5,5];
console.log(arr); //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5, 5, 5, 5]
function noRepeat1(arr) {
for(var i = 0; i < arr.length-1; i++){
for(var j = i+1; j < arr.length; j++){
if (arr[i]===arr[j]){
arr.splice(j,1);
j--;
}
}
}
return arr;
}
var arr2 = noRepeat1(arr);
console.log(arr2); //[1, 23, 3, 5, 6, 7, 9, 8]2. Use the indexOf() method to determine whether the position subscript of the first appearance of this element in the array is equal to the loop subscript
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5,5,5];
console.log(arr); //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5, 5, 5]
function noRepeat2(arr) {
for (var i = 0; i < arr.length; i++) {
if (arr.indexOf(arr[i]) != i) {
arr.splice(i,1);//After deleting the array element, the array length is reduced by 1 and the following elements are moved forward i--;//array subscript rollback}
}
return arr;
}
var newArr = noRepeat2(arr);
console.log(newArr); //[1, 23, 3, 5, 6, 7, 9, 8]3. Using the filter method in the array
var arr = ['apple','banana','pear','apple','orange','orange'];
console.log(arr) //["apple", "banana", "pear", "apple", "orange", "orange"]
var newArr = arr.filter(function(value,index,self){
return self.indexOf(value) === index;
});
console.log(newArr); //["apple", "banana", "pear", "orange"]4. Use the new array to determine the index of the current element in the array through the indexOf method. If it is equal to the subscript of the loop, add it to the new array.
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5,5,5];
console.log(arr) //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5, 5, 5]
function noRepeat4(arr) {
var ret = [];
for (var i = 0; i < arr.length; i++) {
if (arr.indexOf(arr[i]) == i) {
ret.push(arr[i]);
}
}
return ret;
}
var arr2 = noRepeat4(arr);
console.log(arr2); //[1, 23, 3, 5, 6, 7, 9, 8]5. Use empty objects to record the elements already stored in the new array
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5];
console.log(arr) //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5]
var obj={};
var newArr = [];
for(var i=0;i<arr.length;i++){
if(!obj[arr[i]]){
obj[arr[i]]=true;
newArr.push(arr[i]);
}
}
console.log(newArr); //[1, 23, 3, 5, 6, 7, 9, 8]6. With the help of the new array, determine whether the element exists in the new array. If not, add the element to the new array.
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5];
console.log(arr); //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5]
function noRepeat6(arr){
var newArr = [];
for(var i = 0; i < arr.length; i++){
if (newArr.indexOf(arr[i]) == -1) {
newArr.push(arr[i]);
}
}
return newArr;
}
var arr2 = noRepeat6(arr);
console.log(arr2); //[1, 23, 3, 5, 6, 7, 9, 8]7. With the help of the new array, determine whether the element exists in the new array. If not, add the element to the new array (the length of the original array remains unchanged but is sorted in string order)
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5];
console.log(arr); //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5]
function noRepeat7(arr) {
var ret = [],
end; //temporary variable used to compare repeated elements arr.sort(); //re-sort the numbers end = arr[0];
ret.push(arr[0]);
for (var i = 1; i < arr.length; i++) {
if (arr[i] != end) {//If the current element is not equal to the temporary element, add this element to the new array ret.push(arr[i]);
end = arr[i];
}
}
return ret;
}
var arr2 = noRepeat7(arr);
console.log(arr2); //[1, 23, 3, 5, 6, 7, 8, 9]8. This method does not directly change the original array with the help of a new array, and the array after deduplication is sorted
var arr = [1,23,1,1,1,3,23,5,6,7,9,9,8,5];
console.log(arr); //[1, 23, 1, 1, 1, 3, 23, 5, 6, 7, 9, 9, 8, 5]
function noRepeat8(arr) {
var end; //temporary variable used to compare repeated elements arr.sort(); //re-sort the numbers end = arr[0];
for (var i = 1; i < arr.length; i++) {
if (arr[i] == end) {//If the current element is equal to the temporary element, delete this element from the array arr.splice(i,1);
i--;
}else{
end = arr[i];
}
}
return arr;
}
var arr2 = noRepeat8(arr);
console.log(arr2); //[1, 23, 3, 5, 6, 7, 8, 9]9. Double loop changes the original array
var arr = [1,1,2,2,3,3,4,4,5,5,4,3,1,2,6,6,6,6];
console.log(arr); //[1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 4, 3, 1, 2, 6, 6, 6, 6]
function noRepeat9(arr){
for (var i = 0; i < arr.length; i++) {
for (var j = 0; j < arr.length; j++) {
if (arr[i] == arr[j] && i != j) {//Delete the repeated numbers arr.splice(j, 1);
}
}
}
return arr;
}
var arr2 = noRepeat9(arr);
console.log(arr2); //[1, 2, 3, 4, 5, 6]10. With the help of new array
var arr = [1,1,2,2,3,3,4,4,5,5,4,3,2,1,1,1];
console.log(arr); //[1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 4, 3, 2, 1, 1, 1]
var newArr = [];
for (var i = 0; i < arr.length; i++) {
var repArr = []; //Receive the subscript after the repeated data //Inner loop finds the subscript with repeated data for (var j = i + 1; j < arr.length; j++) {
if (arr[i] == arr[j]) {
repArr.push(j);//Find the subscript of the following repeated data}
}
//console.log(repArr);
if (repArr.length == 0) {//If the repeated array has no value, it means it is not repeated data newArr.push(arr[i]);
}
}
console.log(newArr); //[5, 4, 3, 2, 1]11. With the help of the Set structure provided by ES6
var arr = [1,1,2,2,3,3,4,4,5,5,4,3,2,1,1,1];
console.log(arr); //[1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 4, 3, 2, 1, 1, 1]
function noRepeat11(arr){
var newArr = [];
var myset = new Set(arr); //Using the feature that the Set structure cannot receive duplicate data for(var val of myset){
newArr.push(val)
}
return newArr;
}
var arr2 = noRepeat11(arr)
console.log(arr2); //[1, 2, 3, 4, 5]The above are the details of 11 methods for js array deduplication. For more information about js array deduplication, please pay attention to other related articles on 123WORDPRESS.COM! You may also be interested in:
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