A question that must be prepared for the front-end interview: How to remove duplicates of Javascript's Array. As far as I know, Baidu, Tencent, Shanda, etc. have all asked this question in interviews. This question seems simple, but in fact it contains hidden dangers. The test is not only about realizing this function, but also about your in-depth understanding of computer program execution.
Method 1:
Use splice to operate directly on the original array
Double-layer loop, Outer loop elements, when comparing the values
in the inner loop, if the values are the same, delete this value
Note: After deleting the element, you need to change the length of the array Also minus 1.
Array.prototype.distinct = function (){
var arr = this,
i,
j,
len = arr.length;
for(i = 0; i < len; i++){
for(j = i + 1; j < len; j++){
if(arr[i] == arr[j]){
arr.splice(j,1);
len--;
j--;
}
}
}
return arr;
};
var a = [1,2,3,4,5,6,5,3,2,4,56,4,1,2,1,1,1,1,1,1,];
var b = a.distinct();
console.log(b.toString()); //1,2,3,4,5,6,56Advantages: simple and easy to understand
Disadvantages: high memory usage and slow speed
Method 2:
Double-layer loop, outer loop element, compare value during inner loop
If there are the same values, skip them, if not, push them into the array
Array.prototype.distinct = function(){
var arr = this,
result = [],
i,
j,
len = arr.length;
for(i = 0; i < len; i++){
for(j = i + 1; j < len; j++){
if(arr[i] === arr[j]){
j = ++i;
}
}
result.push(arr[i]);
}
return result;
}
var arra = [1,2,3,4,4,1,1,2,1,1,1];
arra.distinct(); //返回[3,4,2,1]Method 3: Use the object’s attributescannot have the same characteristics to remove duplicates
Array.prototype.distinct = function (){
var arr = this,
i,
obj = {},
result = [],
len = arr.length;
for(i = 0; i< arr.length; i++){
if(!obj[arr[i]]){ //如果能查找到，证明数组元素重复了
obj[arr[i]] = 1;
result.push(arr[i]);
}
}
return result;
};
var a = [1,2,3,4,5,6,5,3,2,4,56,4,1,2,1,1,1,1,1,1,];
var b = a.distinct();
console.log(b.toString()); //1,2,3,4,5,6,56Method 4: ArrayRecursionRemove duplication
##Use the idea of recursion Sort first, then compare from the end, if they are the same, delete themArray.prototype.distinct = function (){
var arr = this,
len = arr.length;
arr.sort(function(a,b){ //对数组进行排序才能方便比较
return a - b;
})
function loop(index){
if(index >= 1){
if(arr[index] === arr[index-1]){
arr.splice(index,1);
}
loop(index - 1); //递归loop函数进行去重
}
}
loop(len-1);
return arr;
};
var a = [1,2,3,4,5,6,5,3,2,4,56,4,1,2,1,1,1,1,1,1,56,45,56];
var b = a.distinct();
console.log(b.toString()); //1,2,3,4,5,6,45,56
Method Five: Use indexOf and forEach
Array.prototype.distinct = function (){
var arr = this,
result = [],
len = arr.length;
arr.forEach(function(v, i ,arr){ //这里利用map，filter方法也可以实现
var bool = arr.indexOf(v,i+1); //从传入参数的下一个索引值开始寻找是否存在重复
if(bool === -1){
result.push(v);
}
})
return result;
};
var a = [1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,3,3,3,3,3,3,3,2,3,3,2,2,1,23,1,23,2,3,2,3,2,3];
var b = a.distinct();
console.log(b.toString()); //1,23,2,3
Method 6: Use ES6’s set
Set data structure, which is similar to an array, and the values of its members are all unique. Use Array.from to convert the Set structure into an arrayfunction dedupe(array){
return Array.from(new Set(array));
}
dedupe([1,1,2,3]) //[1,2,3]Expand Operator(...) uses for internally. ..of loop
let arr = [1,2,3,3]; let resultarr = [...new Set(arr)]; console.log(resultarr); //[1,2,3]
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