CODEWITHSUNDEEP
javascriptarrays
dagda1
dagda1

Reputation: 28870

boolean sort for comparator in javascript

I have found the following boolean sort:

  const sorted = things.sort((left, right) => {
    return Number(!!left.current) - Number(!!right.current);
  });

Is this the correct way to sort booleans?

Upvotes: 1

Views: 1486

Answers (3)

Bharata
Bharata

Reputation: 14175

Yes, the best comparator in JavaScript to sort an booleans array is minus comparator, because in this case (mathematical procedure) all booleans (we have only false and true) will be casted into numbers.

You can read it in documentation from Array.sort() function:

compareFunction Optional
Specifies a function that defines the sort order. If omitted, the array is sorted according to each character's Unicode code point value, according to the string conversion of each element.

It is an unicode code point value, which means it is a number.

Example

And I have to mention that you do not need an extra casting to a number like Number(!!boolean).

// We need two arrays to see the difference between
// ascending and descending order because the returned
// array is sorted in place, and no copy is made.
var things1 = [true, false, true, false, true],
    things2 = [true, false, true, false, true];

var sorted_AscendingOrder = things1.sort(function(left, right)
{
    return left - right
});

var sorted_DescendingOrder = things2.sort(function(left, right)
{
    return right - left
});

console.log(sorted_AscendingOrder.join(', '));
console.log(sorted_DescendingOrder.join(', '));

But you could sort an booleans array without of any comparator like follows:

var things3 = [true, false, true, false, true];
// in Ascending Order
console.log(things3.sort().join(', '));

var things4 = [true, false, true, false, true];
// in Descending Order
console.log(things4.sort().reverse().join(', '));

Upvotes: 0

Nina Scholz
Nina Scholz

Reputation: 386700

You could use the difference of the values, casted to boolean.

The minus operator coerces both operands to number and returns a numerical value, which reflects the order as needed by Array#sort.

undefined values are sorted to the end and are never used for sorting callback.

var booleans = [0, true, 42, undefined, null, NaN, 'foo'];

booleans.sort((a, b) => Boolean(a) - Boolean(b)); // falsy values first
console.log(booleans);

booleans.sort((a, b) => Boolean(b) - Boolean(a)); // truthy values first
console.log(booleans);
.as-console-wrapper { max-height: 100% !important; top: 0; }

Upvotes: 0

Mihai Alexandru-Ionut
Mihai Alexandru-Ionut

Reputation: 48407

Why don't just use - operator ? 

things = [{"current":true},{"current":false},{"current":true}]
things.sort((left, right) => left.current - right.current);
console.log(things);

- will coerce both operands to Number automatically.

Upvotes: 2

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