Trying to concat elements within in an array for example:
const x = ['1', '2', '3', '4', '5', '6']
becomes
const x = ['12', '34', '56']
The most straight-forward solution for me would be to manually loop through the array, create a new element, combining current index and index + 1, then splice the array, inserting the new element and removing the 2.
However, I am looking for something more concise if anyone has ever encountered this problem before.
Any help is v much appreciated. Thanks
You could assign to new indices and adjust the length of the array.
const
x = ['1', '2', '3', '4', '5', '6'];
let i = 0;
while (i * 2 < x.length) x[i] = x[i * 2] + x[i++ * 2 + 1];
x.length = i;
console.log(x);First break the array down in chunks.. You can make the chunk size configurable as follows
function chunkify(arr, size) {
let arr2 = [];
let subArr = [];
for (let i = 0; i < arr.length; i += size) {
subArr = arr.slice(i, i + size);
arr2.push(subArr.join(''));
}
return arr2;
}
And then use it like
const x = ['1', '2', '3', '4', '5', '6'];
const y = chunkify(x, 2);
console.log(y); // ['12', '34', '56']
If a non-mutating approach is acceptable, the idea of concatenating odd indexes with their predecessor can be coded fairly concisely with reduce...
const pairsOf = x =>
x.reduce((a,n,i) => (i%2 ? a[a.length-1]+=n : a.push(n), a), []);
console.log(pairsOf(['1', '2', '3', '4', '5', '6']));
console.log(pairsOf(['1', '2', '3', '4', '5', '6', '7']));One could implement an unzip method for list-like structures, and based on that concatenate the unzipped array items via a simple forEach task ...
function unzip(listLike, forceEven = false) {
const arr = Array.from(listLike ?? []);
const left = [];
const right = [];
for (let idx = 0; idx < arr.length; idx = idx + 2) {
left.push( arr[idx] );
if (arr.hasOwnProperty(idx + 1)) {
right.push( arr[idx + 1] );
}
}
if (forceEven === true) {
left.length = right.length;
}
return [ left, right ];
}
let arr = ['1', '2', '3', '4', '5', '6', '7'];
// test of `unzip` implementation.
console.log(
'test of `unzip` implementation ...',
{ arr, unzipped: unzip(arr),
});
// solving the OP's problem.
let right;
{ [arr, right] = unzip(arr, true) };
console.log(
'evenly `unzip` and reassign `arr` ...',
{ arr, right },
);
arr.forEach((item, idx) =>
arr[idx] = item + right[idx]
);
console.log(
'result of unzipped and concatenated `arr` items ...',
{ arr },
);
// solving the OP's problem for an unevenly unzipped array.
arr = ['1', '2', '3', '4', '5', '6', '7'];
right;
{ [arr, right] = unzip(arr) };
console.log(
'unevenly unzipped and reassigned `arr` ...',
{ arr, right },
);
arr.forEach((item, idx) =>
arr[idx] = item + (right[idx] ?? '')
);
console.log(
'result of unevenly unzipped and concatenated `arr` items ...',
{ arr },
);.as-console-wrapper { min-height: 100%!important; top: 0; }