I'm attempting to reverse the flattening process of an array.
The JSON array I have as input contains 4 elements:
[
{
"nestedObj": {
"id":12
}
},
{
"nestedObj": {
"id":555
}
},
{
"nestedObj": {
"id":555
}
},
{
"nestedObj" :{
"id":771
}
}
]
I aim to convert it into an array of arrays, with each sub-array containing elements grouped by their nestedObj.id.
The initial JSON is assumed to be sorted by nestedObj.id.
In the example above, since the id of nestedObj for the 2nd and 3rd elements are the same (555), they will be grouped together in one sub-array.
The resulting array will consist of only 3 sub-array elements:
[
[{
"nestedObj": {
"id":12
}
}],
[{
"nestedObj": {
"id":555
}
},
{
"nestedObj": {
"id":555
}
}],
[{
"nestedObj" :{
"id":771
}
}]
]
This code provides the desired output:
const data = [ /* ...the above input data... */ ];
let result = [];
let prevId = null;
for (let elem of data) {
let currId = elem.nestedObj.id;
if (currId === prevId) {
result[result.length - 1].push({...elem});
} else {
result.push([{...elem}]);
}
prevId = currId;
}
However, the code is quite verbose. It lacks the elegance of modern JavaScript techniques like 'reduce' or other functional programming approaches. Can anyone suggest a sleeker rewrite?