2016-02-02-create-range-0...n-easily-using-one.md

title: Create array sequence [0, 1, ..., N-1] in one line tip-number: 33 tip-username: SarjuHansaliya tip-username-profile: https://github.com/SarjuHansaliya tip-tldr: Compact one-liners that generate ordinal sequence arrays

• /en/create-range-0...n-easily-using-one-line/

Here are two compact code sequences to generate the N-element array [0, 1, ..., N-1]:

Solution 1 (requires ES5)

Array.apply(null, { length: N }).map(Function.call, Number);

Brief explanation

1. Array.apply(null, {length: N}) returns an N-element array filled with undefined (i.e. A = [undefined, undefined, ...]).
2. A.map(Function.call, Number) returns an N-element array, whose index I gets the result of Function.call.call(Number, undefined, I, A)
3. Function.call.call(Number, undefined, I, A) collapses into Number(I), which is naturally I.
4. Result: [0, 1, ..., N-1].

For a more thorough explanation, go here.

Solution 2 (requires ES6)

It uses Array.from https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/from

Array.from(new Array(N), (val, index) => index);

Solution 3 (requires ES6)

Array.from(Array(N).keys());

Brief explanation

1. A = new Array(N) returns an array with N holes (i.e. A = [,,,...], but A[x] = undefined for x in 0...N-1).
2. F = (val,index)=>index is simply function F (val, index) { return index; }
3. Array.from(A, F) returns an N-element array, whose index I gets the results of F(A[I], I), which is simply I.
4. Result: [0, 1, ..., N-1].

One More Thing

If you actually want the sequence [1, 2, ..., N], Solution 1 becomes:

Array.apply(null, { length: N }).map(function (value, index) {
    return index + 1;
});

and Solution 2:

Array.from(new Array(N), (val, index) => index + 1);