Course of Raku / Advanced / More about built-in types / Sets, bags, and mixes

Set operations

Sets can be combined with the usual operations from set theory. Each operator has a Unicode symbol and an ASCII spelling; you can use whichever you prefer.

The union ∪ (or (|)) collects all the values that are in either set:

say (set(1, 2, 3) ∪ set(3, 4, 5)).elems; # 5

The two sets share the value 3, so the union has five distinct elements: 1, 2, 3, 4, 5.

The intersection ∩ (or (&)) keeps only the values that are in both sets:

my $common = set(1, 2, 3) ∩ set(2, 3, 4);
say $common;       # Set(2 3) — note that sets are unordered
say $common.elems; # 2
say 2 ∈ $common;   # True

Here the intersection contains 2 and 3 — the values present in both sets. A set has no inherent order, so the two elements may appear either way round when printed.

The result of these operations is itself a set, so you can ask it the same questions: how many elements it has, and whether a particular value belongs to it.

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