This article will introduce to you two ways to deduplicate arrays in ES6. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.
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Two ways to deduplicate arrays in ES6
Method 1:
function unique(arr) { const res = new Map(); return arr.filter((a) => !res.has(a) && res.set(a, 1)) }
It’s as short as that, let’s explain why.
Map object
Map is a new data structure provided by ES6.
Map objects store key-value pairs. Any value (object or primitive) can be used as a key or a value.
The following table lists the methods of the Map object.
Method | Description |
---|---|
Delete all Key/value pairs, no return value. | |
Delete a key and return true. If deletion fails, return false. | |
Performs the specified operation on each element. | |
Returns the value corresponding to the Map object key. | |
Returns a Boolean value indicating whether a key is in the current Map object. | |
Set the key/value key/value pair for the Map object. |
The filter() method of array
The filter() method creates a new array. The elements in the new array are determined by checking all elements in the specified array that meet the conditions. .Syntax:
array.filter(function(currentValue,index,arr), thisValue)
Parameter description:
Arrow function
return arr.filter((a) => !res.has(a) && res.set(a, 1)) //上面的代码可以改成这样 return arr.filter(function(a){ return !res.has(a) && res.set(a, 1); });
2. This will not be bound.To learn more, click here
Method one analysis
function unique(arr) { //定义常量 res,值为一个Map对象实例 const res = new Map(); //返回arr数组过滤后的结果,结果为一个数组 //过滤条件是,如果res中没有某个键,就设置这个键的值为1 return arr.filter((a) => !res.has(a) && res.set(a, 1)) }
Method two:
function unique(arr) { return Array.from(new Set(arr)) }
The from method of array
Syntax:
Array.from(arrayLike[, mapFn[, thisArg]])
Description | |
---|---|
Required, an array-like object or iterable object that you want to convert to a real array. | |
Optional, if this parameter is specified, the finally generated array will be processed by this function and then returned. | |
Optional, the value of this when executing the mapFn function. |
Sample code:
const bar = ["a", "b", "c"]; Array.from(bar); // ["a", "b", "c"] Array.from('foo'); // ["f", "o", "o"]
Set object
Set object allows you to store A unique value of any type, whether a primitive value or an object reference.A Set object is a collection of values, and you can iterate its elements in the order of insertion.
The elements in the Set will only appear once, that is, the elements in the Set are unique.
Syntax:
new Set([iterable]);
Parameters: iterable, if you pass an iterable object (including Array, Map, Set, String, TypedArray, arguments object, etc.), all its elements will be added to the new Set. If this parameter is not specified or its value is null, the new Set is empty.
Description | |
---|---|
Add someone value, returning the Set object itself. | |
Deletes all key/value pairs and returns no value. | |
Delete a key and return true. If deletion fails, return false. | |
Performs the specified operation on each element. | |
Returns a Boolean value indicating whether a key is in the current Set object. |
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