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 ?
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]
]
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]
]
let tilts = raw.map( ( val ) => val.tilt );