set-iteration.md

Set and Multiset Iteration

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Tools for set and multiset operations on iterables.

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Distinct

Filter out elements from the iterable only returning distinct elements.

Set::distinct(iterable $data, bool $strict = true)

Defaults to strict type comparisons. Set strict to false for type coercion comparisons.

use IterTools\Set;

$chessSet = ['rook', 'rook', 'knight', 'knight', 'bishop', 'bishop', 'king', 'queen', 'pawn', 'pawn', ... ];

foreach (Set::distinct($chessSet) as $chessPiece) {
    print($chessPiece);
}
// rook, knight, bishop, king, queen, pawn

$mixedTypes = [1, '1', 2, '2', 3];

foreach (Set::distinct($mixedTypes, false) as $datum) {
    print($datum);
}
// 1, 2, 3

Distinct By

Filter out elements from the iterable only returning distinct elements according to a custom comparator function.

Set::distinctBy(iterable $data, callable $compareBy)

use IterTools\Set;

$streetFighterConsoleReleases = [
    ['id' => '112233', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'Dreamcast'],
    ['id' => '223344', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'PS4'],
    ['id' => '334455', 'name' => 'Street Fighter 3 3rd Strike', 'console' => 'PS5'],
    ['id' => '445566', 'name' => 'Street Fighter VI', 'console' => 'PS4'],
    ['id' => '556677', 'name' => 'Street Fighter VI', 'console' => 'PS5'],
    ['id' => '667788', 'name' => 'Street Fighter VI', 'console' => 'PC'],
];
$compareBy = fn ($sfTitle) => $sfTitle['name'];

$uniqueTitles = [];
foreach (Set::distinctBy($streetFighterConsoleReleases, $compareBy) as $sfTitle) {
    $uniqueTitles[] = $sfTitle;
}

// Contains one SF3 3rd Strike entry and one SFVI entry.

Intersection

Iterates intersection of iterables.

Set::intersection(iterable ...$iterables)

If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$chessPieces = ['rook', 'knight', 'bishop', 'queen', 'king', 'pawn'];
$shogiPieces = ['rook', 'knight', 'bishop' 'king', 'pawn', 'lance', 'gold general', 'silver general'];

foreach (Set::intersection($chessPieces, $shogiPieces) as $commonPiece) {
    print($commonPiece);
}
// rook, knight, bishop, king, pawn

Intersection Coercive

Iterates intersection of iterables using type coercion.

Set::intersectionCoercive(iterable ...$iterables)

If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$numbers  = [1, 2, 3, 4, 5];
$numerics = ['1', '2', 3];

foreach (Set::intersectionCoercive($numbers, $numerics) as $commonNumber) {
    print($commonNumber);
}
// 1, 2, 3

Partial Intersection

Iterates M-partial intersection of iterables.

Set::partialIntersection(int $minIntersectionCount, iterable ...$iterables)

• If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$staticallyTyped    = ['c++', 'java', 'c#', 'go', 'haskell'];
$dynamicallyTyped   = ['php', 'python', 'javascript', 'typescript'];
$supportsInterfaces = ['php', 'java', 'c#', 'typescript'];

foreach (Set::partialIntersection(2, $staticallyTyped, $dynamicallyTyped, $supportsInterfaces) as $language) {
    print($language);
}
// c++, java, c#, go, php

Partial Intersection Coercive

Iterates M-partial intersection of iterables using type coercion.

Set::partialIntersectionCoercive(int $minIntersectionCount, iterable ...$iterables)

• If input iterables produce duplicate items, then multiset intersection rules apply.

use IterTools\Set;

$set1 = [1, 2, 3],
$set2 = ['2', '3', 4, 5],
$set3 = [1, '2'],

foreach (Set::partialIntersectionCoercive(2, $set1, $set2, $set3) as $partiallyCommonNumber) {
    print($partiallyCommonNumber);
}
// 1, 2, 3

Difference

Iterates the difference of iterables. Returns elements from the first iterable not present in any of the other iterables.

Set::difference(iterable $a, iterable ...$iterables)

If input iterables produce duplicate items, then multiset difference rules apply.

use IterTools\Set;

$a = [1, 2, 3, 4, 7];
$b = [2, 3, 5, 8];
$c = [1, 6, 9];

foreach (Set::difference($a, $b, $c) as $item) {
    print($item);
}
// 4, 7

Difference Coercive

Iterates the difference of iterables using type coercion.

Set::differenceCoercive(iterable $a, iterable ...$iterables)

If input iterables produce duplicate items, then multiset difference rules apply.

use IterTools\Set;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];

foreach (Set::differenceCoercive($a, $b) as $item) {
    print($item);
}
// 4, 7

Symmetric difference

Iterates the symmetric difference of iterables.

Set::symmetricDifference(iterable ...$iterables)

If input iterables produce duplicate items, then multiset difference rules apply.

use IterTools\Set;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];
$c = [1, 2, 3, 6, 9];

foreach (Set::symmetricDifference($a, $b, $c) as $item) {
    print($item);
}
// 1, 4, 5, 6, 7, 8, 9

Symmetric difference Coercive

Iterates the symmetric difference of iterables with type coercion.

Set::symmetricDifferenceCoercive(iterable ...$iterables)

If input iterables produce duplicate items, then multiset difference rules apply.

use IterTools\Set;

$a = [1, 2, 3, 4, 7];
$b = ['1', 2, 3, 5, 8];
$c = [1, 2, 3, 6, 9];

foreach (Set::symmetricDifferenceCoercive($a, $b, $c) as $item) {
    print($item);
}
// 4, 5, 6, 7, 8, 9

Union

Iterates the union of iterables.

Set::union(iterable ...$iterables)

If input iterables produce duplicate items, then multiset union rules apply.

use IterTools\Set;

$a = [1, 2, 3];
$b = [3, 4];
$c = [1, 2, 3, 6, 7];

foreach (Set::union($a, $b, $c) as $item) {
    print($item);
}
//1, 2, 3, 4, 6, 7

Union Coercive

Iterates the union of iterables with type coercion.

Set::unionCoercive(iterable ...$iterables)

If input iterables produce duplicate items, then multiset union rules apply.

use IterTools\Set;

$a = ['1', 2, 3];
$b = [3, 4];
$c = [1, 2, 3, 6, 7];

foreach (Set::unionCoercive($a, $b, $c) as $item) {
    print($item);
}
//1, 2, 3, 4, 6, 7