Generate array from 0 to N with custom increment in Javascript

Question

Problem Description

I am trying to generate an array using keys() and .map() methods, given a preexisting array with length = arrLength, such that only items at a position that are multiples of step are generated. Here is an example,

const arrLength = 20;
const step = 5;

const newArr = [...Array(arrLength).keys() ].map((i) => i + step);

console.log(newArr) ;
// expected: 0,5,10,15,20
// recieved : 5,6,7,...,24

I am particlarly confused as to how to increment the left hand side variable i in map((i) => ... ).

Restrictions

I want to implement this in one line using the keys method and Array and possibly map, so no for loop.

Things I have tried

I tried the following signatures instead

    Array(arrLength).fill().map((_, i) => i+step) ,
    Array.from(Array(arrLength), (_, i) => i+step),
    Array.from({ length: arrLength }, (_, i) => i+step)

but with no success. I have further tried to find a way to increment the i variable using functional syntax but with no success as wel.

I think you should try i*step not +

Servesh Chaturvedi
– Servesh Chaturvedi

2021-09-28 05:01:22 +00:00
Commented Sep 28, 2021 at 5:01 — Servesh Chaturvedi
– Servesh Chaturvedi, Commented Sep 28, 2021 at 5:01

kyun · Accepted Answer · 2021-09-28 04:54:45Z

3

const arrLength = 20;
const step = 5;
const arr = [];
for (let i = 0; i<= arrLength; i+=step){
  arr.push(i);
}
console.log(arr);

Or

const arrLength = 20;
const step = 5;

const newArr = [...Array(Math.floor(arrLength/step) + 1).keys() ].map((i) => i * step);
console.log(newArr);

edited Sep 28, 2021 at 4:54

answered Sep 28, 2021 at 4:53

kyun

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2 Comments

hexaquark Over a year ago

No sorry I cannot use a for loop, I need to do it in one line with keys() method and Array. I will clarify in the post.

kyun Over a year ago

@hexaquark I add another one.

Pascal Tovohery · Accepted Answer · 2021-09-28 07:35:40Z

2

range function work with ES4 Using Array.from can pass an object has property length in it

const range = (start, stop, step) => Array.from({ length: (stop - start) / step + 1}, (_, i) => start + (i * step));
console.log(range(0, 20, 5))

edited Sep 28, 2021 at 7:35

answered Sep 28, 2021 at 5:04

Pascal Tovohery

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1 Comment

Alator Over a year ago

This does not work for ranges in the negative space

Phoenix Himself · Accepted Answer · 2022-05-08 20:47:10Z

0

Stumbled upon this, and while looking at the answers I came up with this. This just basically creates an array with incrementing numbers, but could be extended easily.

This reduce function generates desired array by taking the index i of given element and then we combine what we already got in the previous recursive step (the a variable) with the incremental value i.

const arr = new Array(52).fill(0).reduce((a,_,i) => [...a, i],[])

edited May 8, 2022 at 20:47

Phoenix Himself

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answered May 3, 2022 at 23:32

MI2

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1 Comment

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Chris Kirby · Accepted Answer · 2023-11-04 23:20:29Z

0

I know this is old post but why not just this?

const step = 5;
const result = [...Array(10).keys()].map( i => i * step );

console.log(result);

answered Nov 4, 2023 at 23:20

Chris Kirby

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