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Summary of js array operation methods (must read)

高洛峰Original: 2016-12-06 09:37:371242browse

Judge the odd and even number of occurrences of each number in the numerical array

<!DOCTYPE html> 
<html> 
  <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>

Alibaba written test - array operation - find the different elements in the two arrays

<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>

Array deduplication

Method 1

<!DOCTYPE html> 
<html> 
  <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>

Method 2

<!DOCTYPE html> 
<html> 
  <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>

Method 3

<!DOCTYPE html> 
<html> 
  <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>

Method 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>

Method 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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