5 ways to share how to filter out identical elements from arrays in JavaScript

This article mainly introduces the detailed JavaScriptArray 5 ways to filter the same elements. It also introduces 5 practical methods in detail, which is very practical. Value, friends in need can refer to

Method 1: Compare the value of the inner loop variable.

var arr = [1, 2, 3, 1, 3, 4, 5, 5];
var resultArr = [];
for (i = 0; i < arr.length; i++) {
  for (j = 0; j < resultArr.length; j++) {
    if (resultArr[j] == arr[i]) {
      break;
    }
  }
  if (j == resultArr.length) {
    resultArr[resultArr.length] = arr[i];
  }
}
console.log(resultArr); //1,2,3,4,5

Method two: counting method.

var arr = [1, 2, 3, 1, 3, 4, 5, 5];
var count;
var resultArr = [];
for (i = 0; i < arr.length; i++) {
  count = 0;
  for (j = 0; j < resultArr.length; j++) {
    if (resultArr[j] == arr[i]) {
      count++;
      break;
    }
  }
  if (count == 0) {
    resultArr[resultArr.length] = arr[i];
  }
}
console.log(resultArr); //1,2,3,4,5

Method three: flag method (also called hypothesis method)

var arr = [1, 2, 3, 1, 2, 3, 4, 5, 5];
var resultArr = []; //[1,2,3]
var flag;
for (var i = 0; i < arr.length; i++) {
  flag = true;
  for (j = 0; j < resultArr.length; j++) {
    if (resultArr[j] == arr[i]) {
      flag = false;
      break;
    }
  }
  if (flag) {
    resultArr[resultArr.length] = arr[i];
  }
}
console.log(resultArr);//1,2,3,4,5

Method four : Use the sort() method to sort and compare

var arr = [1, 2, 3, 1, 2, 3, 4, 5, 5];
var resultArr = [];
arr.sort(function (a, b) {
  return a - b;
});
//这个时候arr变成了[1, 1, 2, 2, 3, 3, 4, 5, 5]
for (i = 0; i < arr.length; i++) {
  if (arr[i] != arr[i + 1]) {
    resultArr[resultArr.length] = arr[i];
  }
}
console.log(resultArr);

Method 5: Use the filter() method to filter out duplicate arrays

var arr = [1, 2, 3, 1, 2, 3, 4, 5, 5];
var resultArr;
resultArr = arr.filter(function (item, index, self) {
  return self.indexOf(item) == index;

});
console.log(resultArr);

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