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export class ArrayUtils {
public static range(start: number, end: number, step = 1) {
function* generateRange() {
let x = start - step;
while (x <= end - step) {
yield (x += step);
}
return {
[Symbol.iterator]: generateRange
};
public static zip<T, U>(left: T[], right: U[]): [T, U][] {
return left.map((value, idx) => [value, right[idx]]);
public static groupBy<T>(
xs: Array<T>,
key: (x: T) => string
): { [key: string]: T } {
// Credit: https://stackoverflow.com/a/34890276
return xs.reduce(function(rv, x) {
(rv[key(x)] = rv[key(x)] || []).push(x);
return rv;
}, {});
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