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关于javascript:JavaScript之数组去重

前言

数组去重是很常见的,这里总结一下,本人学过的数组去重的办法

1、数组遍历联合 indexOf

indexOf 办法可返回指定元素在数组中首次呈现的地位, 如果没有,就返回 -1

<script>
    var obj1 = {
        name: 'tom',
        age: 18
    };
    var obj2 = {
        name: 'tom',
        age: 18
    };
    console.log(obj1 == obj2);// false
    // 这里对象的比拟是比拟对象的援用地址是否雷同


    var array = [1, 2, 3, null, 'aa', 'bb', 'aa', 2, 3, {
        name: 'tom',
        age: 18
    }, {
        name: 'cat',
        age: 19
    }, {
        name: 'tom',
        age: 18
    }, undefined, undefined, null]
    
    
    function unique1(arr) {console.time("unique1");// 开始计时,测试程序运行工夫
        let list = []
        for (var i = 0; i < arr.length; i++) {if (list.indexOf(arr[i]) === -1) {list.push(arr[i])
            }
        }
        console.timeEnd("unique1");// 完结计时,输入工夫
        return list;
    }
    console.log(unique1(array));
</script>

2、Set

Set 属于 ES6 提供的新的数据结构

<script>
    //1、Set
    function unique2(arr) {console.time("unique2");
        let list = Array.from(new Set(arr));
        console.timeEnd("unique2");
        return list;
    }
    console.log(unique2(array));
</script>

3、includes

includes 能够用来判断数组中是否蕴含某个元素

<script>
   function unique3(arr) {console.time("unique3");
        let list = []
        for (let i = 0; i < arr.length; i++) {if (!list.includes(arr[i])) {list.push(arr[i])
            }
        }
        console.timeEnd("unique3");
        return list
    }
    console.log(unique3(array));     
</script>

4、reduce 联合 indexOf

reduce 作为数组办法,能够用来数组遍历

<script>
     function unique5(arr) {console.time("unique5");
        let newArr = Array.from(arr).reduce((pre, now) =>
            pre.includes(now) ? pre : [...pre, now], [])
        console.timeEnd("unique5");
        return newArr
    }
    console.log(unique5(map1));
</script>

5、hasOwnProperty

hasOwnProperty 能够判断是否存在对象属性

<script>
    function unique5(arr) {console.time("unique5");
        var obj = {};
        var newArr = arr.filter(function (item, index, arr) {return obj.hasOwnProperty(typeof item + item) ? false : (obj[typeof item + item] = true)
        })
        console.timeEnd("unique5");
        return newArr
    }
    // 后果中,雷同属性值的对象被去重了,阐明 hasOwnProperty 在比拟时,是判断每个元素的值是否雷同
    console.log(unique5(map));
</script>

6、总结

残缺代码

<script>
    var obj1 = {
        name: 'tom',
        age: 18
    };
    var obj2 = {
        name: 'tom',
        age: 18
    };
    console.log(obj1 == obj2); // false
    // 这里对象的比拟是比拟对象的援用地址是否雷同

    var array = [1, 2, 3, null, 'aa', 'bb', 'aa', 2, 3, {
        name: 'tom',
        age: 18
    }, {
        name: 'cat',
        age: 19
    }, {
        name: 'tom',
        age: 18
    }, undefined, undefined, null]

    //1、indexOf
    function unique1(arr) {console.time("unique1"); // 开始计时,测试程序运行工夫
        let list = []
        for (var i = 0; i < arr.length; i++) {if (list.indexOf(arr[i]) === -1) {list.push(arr[i])
            }
        }
        console.timeEnd("unique1"); // 完结计时,输入工夫
        return list;
    }
    var map1 = [1, 2, 3, 4, 4, 'dog', 'cat', 'dog', undefined, null, undefined, null]
    console.log(unique1(array));

    //2、Set
    function unique2(arr) {console.time("unique2");
        let list = Array.from(new Set(arr));
        console.timeEnd("unique2");
        return list;
    }
    console.log(unique2(array));

    //3、includes
    function unique3(arr) {console.time("unique3");
        let list = []
        for (let i = 0; i < arr.length; i++) {if (!list.includes(arr[i])) {list.push(arr[i])
            }
        }
        console.timeEnd("unique3");
        return list
    }
    console.log(unique3(array));

    //4、reduce+indexOf
    function unique4(arr) {console.time("unique4");
        let newArr = Array.from(arr).reduce((pre, now) =>
            pre.includes(now) ? pre : [...pre, now], [])
        console.timeEnd("unique4");
        return newArr
    }
    console.log(unique4(array));

    //5、hasOwnProperty
    function unique5(arr) {console.time("unique5");
        var obj = {};
        var newArr = arr.filter(function (item, index, arr) {return obj.hasOwnProperty(typeof item + item) ? false : (obj[typeof item + item] = true)
        })
        console.timeEnd("unique5");
        return newArr
    }
    console.log(unique5(array));
</script>

从下面几个办法的测试能够看出程序运行工夫大小排序(因为数据太小,运行工夫也小):

hasOwnProperty > reduce + indexOf > includes > indexOf > Set

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