How to invert boolean array?

Question

Is there a cleaner way to invert boolean array?

var myBoolArray=new bool[]{true, true, true, true, true};
bool[] revertedArray=new bool[5];
for(int i=0;i<myBoolArray.Length;i++)
{
    revertedArray[i]=!myBoolArray[i];
}

Atm I'm doing this, but it looks really ugly.

new bool[5], How do you know it's length 5? And why is it not based on the myBoolArray.Lenght? — Drag and Drop
– Drag and Drop, Commented Apr 1, 2021 at 7:05
Honestly, a bool[] is the worst possible way to store bit data (at least without getting silly); in this case, an int (or even a byte) would be vastly preferable, but for unknown-possibly-large lengths (rather than "at most 32", "at most 64", etc) there's BitArray, which also has a Not() method; guess what Not() does! — Marc Gravell
– Marc Gravell, Commented Apr 1, 2021 at 7:19
Eh... this was just an simple example compared to the real code. — Zdravko Boyanov
– Zdravko Boyanov, Commented Apr 1, 2021 at 10:54

ProgrammingLlama · Accepted Answer · 2021-04-01 06:24:39Z

2

There's a neater way using LINQ, though that's about the only benefit:

bool[] invertedArray = myBoolArray.Select(b => !b).ToArray();

answered Apr 1, 2021 at 6:24

ProgrammingLlama

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4 Comments

ProgrammingLlama Over a year ago

@SomeBody It seems that OP wants a new array.

Lukasz Nowakowski Over a year ago

But that allocates new array in memory to do something that can be done in place.

ProgrammingLlama Over a year ago

@LukaszNowakowski But did OP want to do it in place? It's not going to always be the case that you want to mutate the input. In OP's question they had two arrays at the end. I sense people are getting here from another question that was clear about not wanting a new array.

Lukasz Nowakowski Over a year ago

I noticed that right after I sent my reply. But also take into account that bit from his comment "Eh... this was just an simple example compared to the real code". But you're right I stand corrected. Although I wasn't redirected from question you mentioned :-)

Behemoth · Accepted Answer · 2023-07-19 06:19:19Z

0

You can use Array.ConvertAll<TInput, TOutput> which is more performant than LINQ here.

var myBoolArray = new bool[] { true, true, true, true, true };
bool[] invertedArray = Array.ConvertAll(myBoolArray, b => !b);

edited Jul 19, 2023 at 6:19

answered Jul 19, 2023 at 5:39

Behemoth

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6 Comments

Enigmativity Over a year ago

It is not more performant than LINQ. ProgrammingLlama's answer is equally performant. Since myBoolArray is an array then LINQ's Select operator returns an IIListProvider<bool> which will preallocate an array on ToArray().

Behemoth Over a year ago

Please just take a look at this benchmark. Linq is indeed slightly slower. Or what am I missing here?

Enigmativity Over a year ago

That's not a very good benchmark. Here's a better one. It's far more stable. dotnetfiddle.net/RnNaac

Enigmativity Over a year ago

It does show that ConvertAll is faster.

Enigmativity Over a year ago

Try this variation on your benchmark to see why yours was particularly bad. dotnetfiddle.net/fSOUbM

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