Sets & Bags

Immutable collections — a Set of distinct elements, a Bag with counts.

A Set is an unordered collection of distinct elements; a Bag is the same but keeps a count of each. Both are immutable and pair with the set operators.

Set — distinct elements #

set(...) deduplicates. Membership and size are O(1); iteration order is undefined, so sort when you need determinism.

my $s = set(1, 2, 2, 3);
say $s.elems;
say $s.keys.sort;

3
(1 2 3)

Bag — elements with counts #

bag(...) counts occurrences. Subscripting returns an element's count, .total the sum of all counts.

my $b = bag(<a a b>);
say $b.elems;
say $b<a>;
say $b.total;

2
2
3

.elems is the number of distinct keys (2: a and b); .total is the number of items counted (3).

Notes #

• Any list coerces with .Set / .Bag: <a b b c>.Bag builds the bag directly.
• Mix is the third member — like a Bag but with fractional/real weights instead of integer counts.
• These are immutable; their mutable cousins are SetHash and BagHash, which you can add to and remove from.