How to negate all elements in javascript array

Question

What is the shortest way to negate all elements in a javascript array, with reasonable efficiency?

For example, the solution would convert [0, 18, -1, -2, 1, 3] to [0, -18, 1, 2, -1, -3]

The solution does not need to handle any values that are NaN/undefined/null, because the array I need this for does not contain any of those values.

Here is what I normally do (with array array):

for(var i = 0; i < array.length; i++) {
  array[i]*=-1
}

The problem is that I need to invert this array in several places, so don't want to reuse large code.

Thanks

What did you try? Shouldn't have been difficult to at least make an attempt and show that attempt rather than ask how to do it from scratch — charlietfl, Jul 05 '16 at 02:26

Joseph · Accepted Answer · 2016-07-05T02:30:04.223

6

That would be array.map returning the negative of each value. Adding in arrow function for an even shorter syntax.

var negatedArray = array.map(value => -value);

edited Jul 05 '16 at 02:30

answered Jul 05 '16 at 02:22

Joseph

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Nice approach though it gives `-0`. – choz Jul 05 '16 at 02:24
Is -0 any different than 0? – user31415 Jul 05 '16 at 02:25
1

isn't this even simpler `array.map(value => -value);` since, as @AaronJanse points out, he doesn't need to handle nulls or undefineds – mr rogers Jul 05 '16 at 02:28
1

@choz `-0` is different than `+0`. Otherwise, `1/+0` and `1/-0` would also be the same. – Oriol Jul 05 '16 at 02:33
@Oriol Both result in Infinity, even though their binary representation are not same. – choz Jul 05 '16 at 02:39
1

@choz No, `1/+0` is `+Infinity`, and `1/-0` is `-Infinity`. And clearly `+Infinity !== -Infinity`, e.g. `-Infinity < +Infinity`. You can also test `Object.is(+0, -0)`, which produces `false` (they are different). – Oriol Jul 05 '16 at 02:41
2

@Oriol Let's not go to deep.. `+0 === -0` alright.. This [article](http://stackoverflow.com/questions/7223359/are-0-and-0-the-same) might help. – choz Jul 05 '16 at 02:42
There are some features that are bad just because they aren't obvious and cause "bugs" due to user error. One of which is the difference between +0 and -0 – user31415 Jul 05 '16 at 02:52
From now on, I will use this for tons of things, not just negating. – user31415 Jul 05 '16 at 16:22
I have used it like this: `var negatedArray = myArray.map(value => value !== 0 ? -value: value );` To avoid confusion of +/- 0 – HardikDG Jun 25 '17 at 08:49

score 1 · Answer 2 · answered Jul 05 '16 at 03:43

1

negate all elements in a javascript array

I think you are referring to negate only the positive number.

var _myArray = [0, 18, -1, -2, 1, 3]
var _invArray = [];
_myArray.forEach(function(item){
  item >0 ?(_invArray.push(item*(-1))) :(_invArray.push(item))
})
console.log(_invArray);

JSFIDDLE

answered Jul 05 '16 at 03:43

brk

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No, but good solution. `_invArray.push(-Math.abs(item))` could have worked too, if that was what I was looking for – user31415 Jul 05 '16 at 16:22

How to negate all elements in javascript array

2 Answers2