如何提取多维数组中每个子数组的第一个元素？

Question

I have a multidimensional array:

var array 1 = 

[

 [[Name 1, 2, Nigeria], 
  [Name 3, 52, Egypt], 
  [Name 5, 75, South Africa]]

 [[Name 5, 8, Nigeria], 
  [Name 1, 62, Egypt], 
  [Name 3, 115, South Africa]]

 [[Name 6, 88, Nigeria], 
  [Name 3, 92, Egypt], 
  [Name 5, 825, South Africa]]

 ]

I want to have a new flat array:

var array 2 = [Name 1, Name 3, Name 5, Name 5, Name 1, Name 3, Name 6, Name 3, Name 5]

I've tried writing a function that maps over the array and returns the first element:

function name(filteredName){
filteredName.map(function(firstName){
  return firstName[0]
}) 

}

However, this just returns:

[Name 1, Name 1, Name 1] 

I'm really not sure how to solve this! Any help would be great.

Answer 1

You can use nested map() and then flat()

 var arr = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']] ]; const res = arr.map(x => x.map(a => a[0])).flat(2) console.log(res) 

Without flat()

You can do that without using flat() using concat() and spread operator.

 var arr = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']] ]; const res = [].concat(...arr.map(x => x.map(x => x[0]))) console.log(res) 

Answer 2

I loop over the first array. In that loop, I loop over the second one and push the first entry.

 var array = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']], ]; var result = [] for (var i = 0; i < array.length; i++) { for (var j = 0; j < array[i].length; j++) { result.push(array[i][j][0]) } } console.log(result) 

Answer 3

You could use a combination of map and flatMap like this:

 const array1 = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']] ]; const output = array1.flatMap(a => a.map(b => b[0])) console.log(output) 

If flatMap is not supported, you could use a simple nested for...of loop:

 var array1 = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']] ]; var output = []; for (var arr of array1) { for (var arr2 of arr) { output.push(arr2[0]) } } console.log(output) 

Answer 4

You can use Array.flat() and Array.map() like this:

array1.flat().map(arr => arr[0]);

Or you can use Array.concat() instead of Array.flat():

[].concat(...array1).map(arr => arr[0]);

Working example :

 var array1 = [ [ ['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa'] ], [ ['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa'] ], [ ['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa'] ] ]; const NamesArr = array1.flat().map(arr => arr[0]); console.log(NamesArr); console.log('Array.concat():'); console.log([].concat(...array1).map(arr => arr[0])); 

Answer 5

Flatten your array before using .map . That way, you will not be working with a multidimensional array and it will be easier to get the first element of each array:

 var arr = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']] ] console.log(arr.flat().map(item => item[0])) 

Notice

.flat does not have huge support yet, you can either use a polyfill if you want to use the latest code standard or use the spread operator to flatten your array:

 var arr = [ [['Name 1', 2, 'Nigeria'], ['Name 3', 52, 'Egypt'], ['Name 5', 75, 'South Africa']], [['Name 5', 8, 'Nigeria'], ['Name 1', 62, 'Egypt'], ['Name 3', 115, 'South Africa']], [['Name 6', 88, 'Nigeria'], ['Name 3', 92, 'Egypt'], ['Name 5', 825, 'South Africa']] ] console.log([].concat(...arr).map(item => item[0])) 

Answer 6

you could also do it with forEach and spread syntax

var flatArr = [];

array_1.forEach((arr, i) => {
    arr.forEach(innerArr => {
        flatArr = [...flatArr, innerArr[0]]
    })
});