I want to reduce array so I have its' values in 'columns' where the first value lives in the first column, the second one in the second, etc. until it wraps, so that for example the fourth value is in the first of three columns.
>> [1, 2, 3, 4, 5, 6, 7].in_columns(3)
=> [[1, 4, 7], [2, 5], [3, 6]]
A functional one-liner:
a = [1, 2, 3, 4, 5, 6, 7]
cols = 3
res = [...Array(cols).keys()].map(c => a.filter((_, i) => i % cols === c));
console.log(res)You could reduce the array by taking the remainder with the wanted count.
Array.prototype.inColumns = function (count) {
return this.reduce((r, v, i) => ((r[i % count] = r[i % count] || []).push(v), r), []);
}
console.log([1, 2, 3, 4, 5, 6, 7].inColumns(3));.as-console-wrapper { max-height: 100% !important; top: 0; }You can define a new in_columns method for the Array.prototype, using simple for loops:
Array.prototype.in_columns = function(n) {
var result = new Array(n).fill().map(() => []);
for (let i = 0; i < this.length; i++) {
result[i % n].push(this[i]);
}
return result;
}
console.log([1, 2, 3, 4, 5, 6, 7].in_columns(3));You can use below reducer to achieve that
const arr = [1, 2, 3, 4, 5, 6, 7];
const toColums = (arr, count) => {
return [...arr.reduce((a, b, i) => a.set(i % count, (a.get(i % count) || []).concat(b)), new Map).values()];
};
console.log(toColums(arr, 3));