Invert an array of booleans in JavaScript

Question

I am trying to invert the values of a string of boolean values so that instead of

inverted([true, false, true, false, true])

it is [false, true, false, true, false]

So far I have come up with this:

function inverted(bools) {
    var inversion = [];
    var string= [];
    while(!bools) {
      string.push(bools);
    }
    return inversion;
}

But my code is not working, any and all help will be much appreciated!

to be frank there are obvious issues in your code - you update string variable but return inversion array in the end. Also you assume and iterate with a truthy condition. You need to iterate on the array and push an inversion on the boolean. — moha297
– moha297, Commented Mar 31, 2017 at 1:31

guest271314 · Accepted Answer · 2017-03-31 01:25:08Z

6

You can use .map(), ! operator to invert Boolean value, return array of results

function inverted(bools) {
   return bools.map(function(bool) {return !bool})
}

answered Mar 31, 2017 at 1:25

guest271314

1

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5 Comments

guest271314 Over a year ago

If input is actually "[true, false, true, false, true]", inverted("[true, false, true, false, true]".match(/true|false/g).map(eval)) or inverted("[true, false, true, false, true]".match(/true|false/g).map(function(bool){return bool === "true"}))

gyre Over a year ago

You could avoid the need for eval using a look-ahead: inverted("[true, false, true, false, true]".match(/true|(?=false)/g).map(Boolean))

guest271314 Over a year ago

@gyre "[true, false, true, false, true]".replace(/(true)|(false)/g, function(match, p1, p2) {return p1 ? false : true})

gyre Over a year ago

Both valid options, just thought it was worth mentioning :)

guest271314 Over a year ago

@gyre Yes, interesting generation and use of empty string at your approach.

Hari Lamichhane · Accepted Answer · 2017-03-31 01:28:42Z

1

function inverted(bools) {
  for(var i = 0; i < bools.length; i++) {
     bools[i] = !bools[i];
   }
  return bools;
}

Use it as

var bools = [true, false, true];
bools = inverted(bools);

answered Mar 31, 2017 at 1:28

Hari Lamichhane

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Comments

Zibx · Accepted Answer · 2017-03-31 01:30:35Z

1

Your code is just one big mistake. You do not understand basic principles of working with arrays. Do not just use my solution, please read some articles about iterating and getting an element from an array. This one should work:

function inverted(bools) {
  var i, _i, inversion = [];

  for(i = 0, _i = bools.length; i < _i; i++){
    inversion[i] = !bools[i];
  }
  return inversion;
}

answered Mar 31, 2017 at 1:30

Zibx

1044 bronze badges

4 Comments

Zibx Over a year ago

@RobbyCornelissen, I usually optimize my code for performance. My code with for is 12 times faster in Chrome than your code with map. jsperf.com/inverting-an-array

guest271314 Over a year ago

@RobbyCornelissen The previous comment could be two comments. The first including the first two sentences, the second the remainder of sentences; in order to not detract from the former. Or, only first two sentences, omitting remainder of comment.

Robby Cornelissen Over a year ago

@guest271314 You're right. I think that the tone of the first two sentences of this answer put me in a bit of an indignant mood. I'll rewrite my comment.

Robby Cornelissen Over a year ago

@Zibx Point taken, my comment was out of line. On Chrome your code indeed runs 12 times as fast and on Firefox almost twice as fast.

Robby Cornelissen · Accepted Answer · 2017-03-31 01:33:05Z

1

You can do it like this:

Convert the string to a JavaScript array using JSON.parse().
Invert all the booleans using Array.prototype.map();
Convert back to a string using JSON.stringify().

const booleans = "[true, false, true, false, true]";
const inverted = JSON.stringify(JSON.parse(booleans).map(b => !b));

console.log(inverted);

If by a "string", you actually mean an array, you don't need to convert to/from a string and can just do:

const booleans = [true, false, true, false, true];
const inverted = booleans.map(b => !b);

edited Mar 31, 2017 at 1:33

answered Mar 31, 2017 at 1:26

Robby Cornelissen

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Comments

gyre · Accepted Answer · 2017-03-31 02:01:26Z

1

Though many answers here are already great, I thought I would chip in my "golfed" regex solution:

function inverted (b) {
 return b.map(/f/.test, /f/)
}

console.log(
  inverted([true, false, true, false])
)

answered Mar 31, 2017 at 2:01

gyre

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Comments

Joe H · Accepted Answer · 2017-03-31 01:35:18Z

0

You need to split up bools with bools.split(). Then you can check and invert them. You also are not putting anything in inversion[] prior to returning it. Something like the below should work:

function inverted(bools) {
var inversion = [];
var string= bools.split(",");
for(var i=0; i<string.length(); i++) {
  inversion.push(string[i]);
}

return inversion;

}

answered Mar 31, 2017 at 1:35

Joe H

1

Comments

kourouma_coder · Accepted Answer · 2017-03-31 01:39:40Z

0

This is another way to achieve that :

var booleans = [true, false, true, false, true];

function inverted(bools) {
    var inversion = [],i=0;

    while(i< bools.length) {
      inversion.push(!(bools[i]));
      i++;
    }
    return inversion;
}

var inverted =  inverted(booleans);

console.log(inverted);//Outpu : [false, true, false, true, false]

answered Mar 31, 2017 at 1:39

kourouma_coder

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Comments

Guilherme Oliveira · Accepted Answer · 2021-08-09 19:50:37Z

0

let myArray = [true, false, false, true]
// single line solution:
let invertedArray = myArray.map((bool) => !bool)

console.log(invertedArray)

answered Aug 9, 2021 at 19:50

Guilherme Oliveira

433 bronze badges

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