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!

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

Answer 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);

• hatched: Thanks for the solution! How do I modify the codes if I have more elements in each array of codes array ?
• Robby Cornelissen: Updated the answer to allow for more elements.
• hatched: 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'],