JS array merging, de duplication, dimensionality reduction (es6: extended operator, set)

js Array merge 、 duplicate removal 、 Dimension reduction

1. Merge

1.1 Use concat() Merge arrays

function get_concat(collection_a, collection_b) {
    
  return collection_a.concat(collection_b)
}

1.2 Use …( Extension operator ) Merge arrays

function get_concat(collection_a, collection_b) {
    
  return [...collection_a,...collection_b]
}

2. duplicate removal

2.1 Use for

  function get_union(array) {
    
    let temp = [] 
    for (let i = 0; i < array.length; i++) {
    
      if (temp.indexOf(array[i]) == -1) {
    
        temp.push(array[i])
      }
    }
    return temp
  }

2.2 Use the extension operator 、Set

function get_union(collection) {
    
  return [...new Set(collection)]
}

The train of thought is array=> Set => array

1. array=> Set
   new Set(array)
2. The second step Set => array
   […Set]

ps:ES6 Provides a new data structure Set. It's like an array , But the values of the members are unique , There are no duplicate values .
A little set in Mathematics The opposite sex It means ： In a collection , Any two elements are considered different , That is, each element can only appear once .

3. Dimension reduction

drop 2 Dimension group reduced to 1 dimension , Use flat()

function double_to_one(collection) {
    
  return collection.flat();
}

3.1 flat() Method

flat() Method recursively traverses the array at a specified depth , And all the elements and the elements in the traversed sub array are merged into a new array to return .
grammar

var newArray = arr.flat([depth])

Parameters
depth Optional
Specifies the depth of the structure to extract the nested array , The default value is 1.
Return value
A that contains all the elements in the array and subarray New array .