数组去重与深浅拷贝

数组去重

1， 数组去重

• ES6的set 方法

var arr = [1, 2, 2, 3, 5, 6, 3, 7, 4]
var arrCopy = new Set(arr); // [1, 2, 3, 5, 6, 7, 4]

• 对象属性存在的特性，如果没有该属性则存入新数组

var arr =[1, 2, 2, 3, 5, 6, 3, 7, 4]
function unique(arr) {
    var obj={ }
    var newArr=[ ]
    for ( let i = 0; i < arr.length; i++ ) {
        if ( !obj[arr[i]] ) {
            obj.push(arr[i])
            newArr.push(arr[i])
        }
    }
    return newArr
}
console.log(unique(arr)); // [1, 2, 3, 5, 6, 7, 4]

• indexof 方法

var arr =[1, 2, 2, 3, 5, 6, 3, 7, 4]
function unique(arr) {
    var newArr = []
    for (var i = 0; i < arr.length; i++) {
         if (newArr.indexOf(arr[i])===-1) {
             newArr.push(arr[i])
        }
    }
    return newArr
}
console.log(unique(arr)); // [1, 2, 3, 5, 6, 7, 4]

• 利用includes

var arr =[1, 2, 2, 3, 5, 6, 3, 7, 4]
function unique(arr) {
  if (!Array.isArray(arr)) {
    return
  }
  var array =[];
  for(var i = 0; i < arr.length; i++) {
      if( !array.includes( arr[i]) ) { //includes 检测数组是否有某个值
          array.push(arr[i]);
       }
  }
  return array
}

拷贝数组

• ES6中扩展运算符(不去重，但是浅拷贝，是引用不是复制)

var arr =[1, 2, 2, 3, 5, 6, 3, 7, 4]
var arrCopy = [...arr]
arrCopy

• for循环浅拷贝

array = [1,2,3,4,5,6]; 
array2 = [ ]; 
for ( i = 0; i < array.length; i++) { 
    array2[i] = array[i];
}
array2 // [1,2,3,4,5,6]; 

• while() 浅拷贝

array = [1,2,3,4,5,6]; 
array2 = [ ]; 
i = -1
while ( ++i < array.length ) { 
    array2[i] = array[i]
}
array2 // [1,2,3,4,5,6]; 

• array.map() 浅拷贝

array = [1,2,3,4,5,6]; 
array2 = array.map(x=>x)
array2 //  [1,2,3,4,5,6];

• array.filter() 浅拷贝

array = [1,2,3,4,5,6]; 
array2 = array.filter(()=>true)
array2 //  [1,2,3,4,5,6];

• array.slice() 浅拷贝

array = [1,2,3,4,5,6]; 
array2 = array.slice()
array2 //  [1,2,3,4,5,6];

• array.concat (浅拷贝)

array = [2,3,4,5,6]; 
array2 = [4,5,9,10,21]; 
array.concat(array2) // [2, 3, 4, 5, 6, 4, 5, 9, 10, 21]

• array.from (浅拷贝)

array = [2,3,4,5,6]; 
array2 = [ ]; 
array2 = Array.from(array) // [2,3,4,5,6]

• json格式转换(深拷贝)

json.stringify( ) // 将对象、数组转换成字符串
json.parse( ) // 将字符串转成json对象