在 JavaScript 中展平嵌套数组

Question

I have a horrible looking array which looks like this:

EDIT:

array = [
    {
        Letters: [{ Letter: 'A' }, { Letter: 'B' }, { Letter: 'C' }],
        Numbers: [{ Number: '1' }, { Number: '2' }, { Number: '3' }]
    },
    null,
    {
        Letters: [{ Letter: 'D' }, { Letter: 'E' }, { Letter: 'F' }, { Letter: 'G' }, { Letter: 'H' }],
        Numbers: [{ Number: '4' }, { Number: '5' }, { Number: '6' }, { Number: '7' }]
    }
];

And want the array to look like this:

flattenedArray = [a,b,c,1,2,3,d,e,f,g,h,4,5,6,7]

Unfortunately I cannot change the original formatting because that is the form received when merging two API responses that I am getting.

I have tried using:

var flattenedArray = [].concat.apply([], array);

But it just presents the array in the same format it was entered in.

I was wondering if anybody had any advice?

EDIT: I have tried implementing the suggestions given - thank you so much for your help. It seems it is a problem with the format of the list - unfortunately using the chrome console which is in a 'tree' format I cannot see the direct structure of the array output.

Thank you for all your help! EDIT 2: See above for the actual array, thank you for showing me how to see this!

Answer 1

If you have lodash , you can use:

_.flattenDeep(array)

You can also checkout their source code for ides on how to implement yourself if you prefer.

Answer 2

You can create recursive function using forEach() that will return new array.

 var array = [[['a','b','c'],[1,2,3]],[],[['d','e','f','g','h'],[4,5,6,7]]] function flat(data) { var r = [] data.forEach(e => Array.isArray(e) ? r = r.concat(flat(e)) : r.push(e)); return r; } console.log(flat(array)) 

You can also use reduce() instead of forEach()

 var array = [[['a','b','c'],[1,2,3]],[],[['d','e','f','g','h'],[4,5,6,7]]] function flat(data) { return data.reduce((r, e) => Array.isArray(e) ? r = r.concat(flat(e)) : r.push(e) && r, []) } console.log(flat(array)) 

As @Bergi suggested you can use reduce() like this.

data.reduce((r, e) => r.concat(Array.isArray(e) ? flat(e) : [e]), [])

Answer 3

Edit for the new request of nested arrays/objects and the flattening, you could use a combined approach with testing for the type of an element.

 var array = [{ Letters: [{ Letter: 'A' }, { Letter: 'B' }, { Letter: 'C' }], Numbers: [{ Number: '1' }, { Number: '2' }, { Number: '3' }] }, null, { Letters: [{ Letter: 'D' }, { Letter: 'E' }, { Letter: 'F' }, { Letter: 'G' }, { Letter: 'H' }], Numbers: [{ Number: '4' }, { Number: '5' }, { Number: '6' }, { Number: '7' }] }], result = array.reduce(function iter(r, a) { if (a === null) { return r; } if (Array.isArray(a)) { return a.reduce(iter, r); } if (typeof a === 'object') { return Object.keys(a).map(k => a[k]).reduce(iter, r); } return r.concat(a); }, []); console.log(result); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Old request and the immortal question how to flat a nested array.

 var flat = (r, a) => Array.isArray(a) ? a.reduce(flat, r) : r.concat(a), inputArray = array = [[['a', 'b', 'c'], [1, 2, 3]], [], [['d', 'e', 'f', 'g', 'h'], [4, 5, 6, 7]]], outputArray = inputArray.reduce(flat, []); console.log(outputArray); 

Answer 4

You could try the flatten function in Ramda .

  R.flatten([1, 2, [3, 4], 5, [6, [7, 8, [9, [10, 11], 12]]]]);
    //=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

Answer 5

It's nice to use a recursive function for such cases:

 arr = [[['a','b','c'],[1,2,3]],[],[['d','e','f','g','h'],[4,5,6,7]]]; function flatten(arr) { var result = []; for (var i = 0, len = arr.length; i < len; i++) { result = result.concat(Array.isArray(arr[i])? flatten(arr[i]) : [arr[i]]); } return result; } console.log(flatten(arr)); 

Answer 6

Your Array format is not correct, you are missing commas(,) . This is correct array.

var array = [[['a','b','c'],[1,2,3]],[],[['d','e','f','g','h'],[4,5,6,7]]];

 var array = [[['a','b','c'],[1,2,3]],[],[['d','e','f','g','h'],[4,5,6,7]]]; var result = flatten(array); function flatten(array) { var flat = []; if(array !== undefined){ var flat = []; for (var i = 0; i < arguments.length; i++) { if (arguments[i] instanceof Array) { flat = flat.concat(flatten.apply(null, arguments[i])); } else { flat.push(arguments[i]); } } } return flat; } console.log(result); 

Answer 7

No one thought of splicing in-place?

function flatten(array){
    for (var i = 0; i < array.length; i++) {
        if(array[i] instanceof Array){
            array.splice.apply(array,[i,1].concat(array[i]));
            i--;
        }
    };
    return array;
}

One iteration, no recursion.

Answer 8

function steamrollArray(arr) {
  var tmp = [];
  arr.forEach(function(val){
    if(Array.isArray(val))
      tmp = tmp.concat(steamrollArray(val));
    else
      tmp.push(val);
  });

  console.log(tmp);
  return tmp;
}

steamrollArray([1, [2], [3, [[4]]]]);

Answer 9

let arr = [1,2,[3,4]]

/* let newarr = arr.flat(); */

let newarr = Object.values(arr);
let arr2 = []
for(let val of Object.values(arr)) {
         if(!Array.isArray(val)){
     console.log(val)
     arr2.push(val)
     }    
           for ( let val2 of Object.values(val)){
             arr2.push(val2)
           }
}
console.log(arr2)

Answer 10

Implement flatten function using recursion and spread operator.