js array merging, deduplication, dimensionality reduction (ES6: extension operator, Set)

js array merge, deduplication, dimensionality reduction

1. Merge

1.1 Use concat() to merge arrays

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

1.2 Use ... (spread operator) to merge arrays

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

2. Deduplication

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 Using spread operator, Set

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

The idea 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 is similar to an array, but the values ​​​​of the members are all unique, and there are no duplicate values. A bit of the meaning of the heterogeneity
of sets in mathematics : in a set, any two elements are considered to be different, that is, each element can only appear once.

3. Dimensionality reduction

Reduce the 2-dimensional array to 1-dimensional, use flat()

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

3.1 flat() method

The flat() method will recursively traverse the array according to a specified depth, and combine all elements with the elements in the traversed sub-array to return a new array.
grammar

var newArray = arr.flat([depth])

The parameter
depth is optional
to specify the structure depth of the nested array to be extracted, and the default value is 1.
Return Value A new array
containing all the elements in the array and subarrays .