javascript - create multidimensional array from another multidimensional array

Question

I need to generate a multidimensional array from a multidimensional array.
For example, my array:

var codes = [

['2', '12521'],
['3', '32344'],
['3', '35213'],
['4', '42312'],
['4', '41122'],
['5', '51111']

];

And my new array should have this structure:

[0] => Array
    (
        [0] => Array
            (
               [0] => '2'
               [1] => '12521'
            }
    )  
[1] => Array
    (
        [0] => Array
            (
               [0] => '3'
               [1] => '32344'
            }
        [1] => Array
            (
               [0] => '3'
               [1] => '35213'
            }
    )  
[2] => Array
    (
        [0] => Array
            (
               [0] => '4'
               [1] => '42312'
            }
        [1] => Array
            (
               [0] => '4'
               [1] => '41122'
            }
    )  
...

I have been trying to use for looping to populate the new array but have been struggling to do it. Please help. Thanks!

"I have been trying to use for looping..." - You've forgotten to post the relevant code. — Andreas
– Andreas, Commented Nov 21, 2019 at 7:38
Is this just nesting each of the inner arrays into a new array, or am I misreading? Can you clarify? — VLAZ
– VLAZ, Commented Nov 21, 2019 at 7:43
@VLAZ They're grouped based on the first element in the 2-element arrays. — Robby Cornelissen
– Robby Cornelissen, Commented Nov 21, 2019 at 7:44
@RobbyCornelissen OK, this makes more sense. I find that expected representation hard to read. — VLAZ
– VLAZ, Commented Nov 21, 2019 at 7:45
@VLAZ it is based on the first element (single digit) of each arrays , such as 2,3,4,5 — hatched
– hatched, Commented Nov 21, 2019 at 7:45

Robby Cornelissen · Accepted Answer · 2019-11-21 07:57:56Z

1

You could use a simple reduce() operation that keeps track of the current value you're basing your grouping on:

const codes = [
  ['2', '12521'],
  ['3', '32344'],
  ['3', '35213'],
  ['4', '42312'],
  ['4', '41122'],
  ['5', '51111', '']
];

const output = codes.reduce(({result, current}, [x, ...y]) => {
  if (current !== x) result.push([]);
  result[result.length - 1].push([x, ...y]);
  
  return {result, current: x};
}, {result: []}).result;

console.log(output);

edited Nov 21, 2019 at 7:57

answered Nov 21, 2019 at 7:42

Robby Cornelissen

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3 Comments

hatched Over a year ago

Thanks for the solution! How do I modify the codes if I have more elements in each array of codes array ?

Robby Cornelissen Over a year ago

Updated the answer to allow for more elements.

hatched Over a year ago

I'm not sure why the output return me the exactly same row of array to me , my real data has 5 elements in a single array , such as ['R', '2' , '115' , 'AB' ,'117'],

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