Get from one number to another number

Question

Given a number, say 1.2, is there a simple way in JavaScript, to get to -1.5 in steps of .1. Or from say -50.3 to 12.3.

I'm trying to figure out if there is an easier way of doing this then writing a bunch of complex if statements.

Use a `for` loop? But watch out for floating point inaccuracy. — Barmar, Sep 18 '20 at 00:26
@GirkovArpa = given 1.2 as the start value and -1.5 as the end value, then the result would be 1.1,1.0,.9,.8.... to -1.5 — Scott Paterson, Sep 18 '20 at 00:27
The only `if` statement you need is to test whether you're going up or down. You can use different loops depending on the direction. — Barmar, Sep 18 '20 at 00:27
Does this answer your question? [I have min and max number how can I generate n number of array](https://stackoverflow.com/questions/63842169/i-have-min-and-max-number-how-can-i-generate-n-number-of-array) — GirkovArpa, Sep 18 '20 at 00:29
@JohnMontgomery He wants to generate an array of numbers from `x` to `y` in increments of `z`. — GirkovArpa, Sep 18 '20 at 00:30
@GirkovArpa That question is about knowing the number of steps and determining the delta. In this question the delta is known. — Barmar, Sep 18 '20 at 00:30
@GirkovArpa I don't see anything about arrays in the question. — John Montgomery, Sep 18 '20 at 00:31
@JohnMontgomery The OP has posted the example output of: `1.1,1.0,.9,.8...-1.5` — GirkovArpa, Sep 18 '20 at 00:35

score 2 · Accepted Answer · answered Sep 18 '20 at 00:36

To avoid accumulating floating point inaccuracies (see Is floating point math broken?) it would be best to multiply your numbers by 10 and then use steps of 1. You can then divide by 10 when generating the results.

Then you just need two for loops: one for counting up, the other for counting down.

function range(start, end) {
  start = Math.round(start * 10);
  end = Math.round(end * 10);
  result = [];
  if (start > end) { // counting down
    for (let i = start; i >= end; i--) {
      result.push(i / 10);
    }
  } else { // counting up
    for (let i = start; i <= end; i++) {
      result.push(i / 10);
    }
  }
  return result;
}

console.log(range(1.2, -1.5));
console.log(range(-50.3, 12.3));

Thanks Barmar - exactly what I just spent the last few hours trying to get working! — Scott Paterson, Sep 18 '20 at 00:41

score 1 · Answer 2 · answered Sep 18 '20 at 00:48

for (let number = -10.5; number < 10.5; number += 0.1) {
    realPart = number - (number - Math.floor(number));
    decimalPart = Math.floor((number - Math.floor(number)) * 10) / 10;
    console.log( realPart + decimalPart);
}

// or

for (let number = 10.5; number > -10.5; number -= 0.1) {
    realPart = number - (number - Math.floor(number));
    decimalPart = Math.floor((number - Math.floor(number)) * 10) / 10;
    console.log( realPart + decimalPart);
}

Get from one number to another number

2 Answers2