1

Sorry I don't know how to word that title.
I want to transform the following data structure :

raw = [
   {'id': 1, 'tilt': [tilt1_1, ..., tilt9_1]},
   {'id': 2, 'tilt': [tilt1_2, ..., tilt9_2]},
   ...
   {'id': n, 'tilt': [tilt1_n, ..., tilt9_n]},
];

Into :

tilts = [
    [tilt1_1, ..., tilt1_n],
    [tilt2_1, ..., tilt2_n],
    ...
    [tilt9_1, ..., tilt9_n],
];

I have the following working solution:

tilts = [[], [], [], [], [], [], [], [], []];
for (let i = 0; i < raw.length; i++) {
  for (let j = 0; j < tilts.length; j++) {
    tilts[j].push(raw[i]['tilt'][j]);
  }
}

Is there a cleaner or more idiomatic way of achieving this ?

rochard4u
  • 629
  • 3
  • 17
  • 1
    Related/duplicate: [Transposing a 2D-array in JavaScript](https://stackoverflow.com/questions/17428587/transposing-a-2d-array-in-javascript). According to that something like `raw[0].tilt.map((_, i) => raw.map(row => row.tilt[i]))` would work, as long as the dimensions are the same in both directions. – Felix Kling Aug 11 '22 at 13:52
  • That certainly solve the issue. As a beginner in javascript, I was wondering if this solution made the code less readable however. – rochard4u Aug 11 '22 at 14:03
  • 1
    I don't think it would be obvious to anyone (beginner or not) what the purpose of that code is. It should be put inside an appropriately named function, including a helpful comment if you can't assume that readers will understand what *transpose* means in that context. – Felix Kling Aug 11 '22 at 19:38

1 Answers1

1

The thing you're asking for is an array transpose, it can be done in this way:

[
    { 'id': 1, 'tilt': [1.1,1.2,1.3] },
    { 'id': 2, 'tilt': [2.1,2.2,2.3] },
    { 'id': 3, 'tilt': [3.1,3.2,3.3] },
].map(e => e.tilt)                            // isolate the tilt property
 .map((_, i, arr) => arr.map(row => row[i])); // transpose the array

The result will be:

[
    [1.1, 2.1, 3.1], 
    [1.2, 2.2, 3.2], 
    [1.3, 2.3, 3.3]
]

Edit:

If elements are missing in the array, you can filter them out:

[
    { 'id': 1, 'tilt': [1.1] },
    { 'id': 2, 'tilt': [2.1, 2.2] },
    { 'id': 3, 'tilt': [3.1, 3.2, 3.3] },
].map(e => e.tilt)
 .map((_, i, arr) => arr.map((row) => row[i]).filter(e => e))

// result
[
    [1.1], 
    [2.1, 2.2], 
    [3.1, 3.2, 3.3]
]
Benoît P
  • 3,179
  • 13
  • 31