js数组操作方法总结(必看篇)

判断数值数组中各个数字出现的奇偶次数

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>数组操作</title>
  </head>
  <body>
  <script type="text/javascript">
    var arr=[3,1,2,2,1,3,1];
    var sum=[];
    var res=[];
    var count=0;
    var temp;
    for(var i=0;i<arr.length;i++){
      if(res.indexOf(arr[i])==-1){
        res.push(arr[i]);
      }
    }
    for(var i=0;i<res.length;i++){
      for(var j=0;j<arr.length;j++){
        if(arr[j]==res[i]){
          count++;
        }
      }
      sum.push(count);
      count=0;
    }
    console.log(res);//[3,1,2]
    for(var i=0;i<res.length;i++){
      var str=(sum[i]%2==0)?"偶数":"奇数";
      console.log(res[i]+"出现了"+sum[i]+"次");
      console.log(res[i]+"出现了"+str+"次");
    }
  </script>
  </body>
</html> 

阿里笔试-数组操作-找出两个数组中不同的元素

<script type="text/javascript">
  function diff(arr1,arr2){
  var ress = [];
  var arr = arr1.concat(arr2);
  for(var i=0,len=arr.length;i<len;i++){
     if((arr1.indexOf(arr[i])>=0 && arr2.indexOf(arr[i])<0) || (arr1.indexOf(arr[i])<0 && arr2.indexOf(arr[i])>=0)){
        ress.push(arr[i]);
     }
  }
  return ress;
}
var arr1 = [1,2,3,5,7,6];
var arr2 = [1,2,5];
var res = diff(arr1,arr2);
console.log(res);//[3, 7, 6]
</script> 

数组去重

方法1

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>数组去重01</title>
  </head>
  <body>
  <script type="text/javascript">
  //给数组原型添加方法
    Array.prototype.unique = function(){
      var arr = [];
      for(var i=0,i=this.length;i<len;i++){
        if(arr.indexOf(this[i]) == -1){
          arr.push(this[i]);
        }
      }
      return arr;
    };
    console.log([1,2,3,2,5,6,3].unique());//[1, 2, 3, 5, 6]
  </script>
  </body>
</html> 

方法2

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>数组去重02</title>
  </head>
  <body>
  <script type="text/javascript">
    Array.prototype.unique = function(){
    var n = {},
        r=[]; //n为哈希表，r为临时数组
    for(var i = 0; i < this.length; i++) //遍历当前数组
    {
      if (!n[this[i]]) //如果hash表中没有当前项
      {
        n[this[i]] = true; //存入哈希表
        r.push(this[i]); //把当前数组的当前项push到临时数组里面
      }
    }
    return r;
  }
  console.log([1,2,3,2,5,6,3].unique());//[1, 2, 3, 5, 6]
  </script>
  </body>
</html> 

方法3

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>数组去重</title>
  </head>
  <body>
  <script type="text/javascript">
    Array.prototype.unique = function(){
      var arr = [this[0]];//结果数组
      for(var i=1;i<this.length;i++){//从第二项开始遍历
        if(this.indexOf(this[i]) == i){
      //如果当前数组的第i项在当前数组中第一次出现的位置不是i，那么表示第i项是重复的，忽略掉。否则存入结果数组
          arr.push(this[i]);
        }
      }
      return arr;
    }
    console.log([1,2,3,4,2,3,4].unique());// [1, 2, 3, 4]
  </script>
  </body>
</html> 

方法4

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>filter</title>
  <link rel="stylesheet" href="">
</head>
<body>
<script type="text/javascript">
var arr = [4,5,3,2,3,4,5,1];
function fn(num){
  var res = num.filter(function(item,index,array){
    return num.indexOf(item) === index;//num.indexOf(item)将会返回元素在数组第一次出现的位置
    //对于多次出现的元素，除第一次外，其他情况都返回false
  });
  return res;
}
console.log(fn(arr));//[4, 5, 3, 2, 1]
</script>
</body>
</html> 

方法5

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Object 对象来当做哈希表</title>
  <link rel="stylesheet" href="">
</head>
<body>
<script type="text/javascript">
function unique(a) {
 var obj = {};
 return a.filter(function(item) {//filter会返回true的项组成的成员
  return obj.hasOwnProperty(item) ? false : (obj[item] = true);
 });
} 

var a = [1, 1, 3, 2, 1, 2, 4];
var res = unique(a);
console.log(res); // [1, 3, 2, 4]
</script>
</body>
</html> 

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