CODEWITHSUNDEEP
javascriptarraysnode.jsbinaryboolean
SCLeo
SCLeo

Reputation: 383

Using binary to compress boolean array

I am wondering if there is a way that allows me to store a boolean array efficiently. In my understanding, every boolean variable in JavaScript takes 1 byte or 8 bits to store. However, if I want to store a array of boolean value, 8 bits can store up to 8 boolean values actually. The rest 7 bits are wasted.

In language like C or Java, people can use bit operation like ">>", "~" to store boolean array into a int value. However, that does not work well in JavaScript since it works extremely slow in JavaScript because it needs to convert the floating number to int (See this question).

I also noticed Buffer in JavaScript which stores binary data directly. However, I cannot find a way to use it to store boolean array. I think Buffer are more focused on encoding stuff. For example, if I want to set the fifth bit of a boolean array to true, I can do data |= 1<<4 but I cannot find a way to do so in Buffer.

Any solution?

Upvotes: 1

Views: 4117

Answers (4)

Garen
Garen

Reputation: 177

Take a look at this amazing answer: https://www.smashingmagazine.com/2011/10/optimizing-long-lists-of-yesno-values-with-javascript/

Convert the array of Boolean to 1’s and 0’s and join them as a string. For further optimization, you can represent 16 bit chunks as 1 UTF-16 character for 93% compression and store that string. It’s actually quite easy.

Upvotes: 0

Alec Mev
Alec Mev

Reputation: 4813

As an alternative to the accepted answer, there's also minimal-bit-array, which ndarray-bit is based on, both made by the creator of ndarray itself. Very similar usage (from readme):

var x = new BitArray(100)
x.set(5, true)
console.log(x.get(4)) // Prints false
console.log(x.get(5)) // Prints true

Upvotes: 2

idk lol
idk lol

Reputation: 11

Is this what you mean? (Max index is 30):

function BoolArray(){
  this.arr = 0;
}

BoolArray.prototype.get = function(idx){
  return !!((this.arr >> idx) & 1)
}

BoolArray.prototype.set = function(idx, val){
  this.arr |= (val & 1) << idx;
}

Upvotes: 1

stdob--
stdob--

Reputation: 29167

You can use a Bit-Vector implementation:

var bs = new BitSet;
bs.set(128, 1); // Set bit at position 128
console.log(bs.toString(16)); // Print out a hex dump with one bit set

Upvotes: 4

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