Methods by type

Hash operations

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Accumulate multiple values per key with .push, and the (Hash-backed) Map type.

Beyond plain key/value storage, .push accumulates several values under one key, turning it into an array. Raku's immutable Map type also exists, though Raku++ backs it with a Hash (see the note).

push — multiple values per key #

.push on a hash adds to a key; pushing a second value under the same key promotes it to an array of values.

my %h;
%h.push("a" => 1);
%h.push("a" => 2);
say %h<a>;

Output

[1 2]

This is the idiom for grouping — collect everything that shares a key.

Map — the immutable hash #

Map is the immutable sibling of Hash: build it once and read from it. Its type is distinct from Hash.

my $m = Map.new("a", 1, "b", 2);
say $m<a>;
say $m.^name;

Output

1
Map

Notes #

.push differs from assignment: %h<a> = 2 replaces, while %h.push("a" => 2) accumulates into an array once there's more than one value.
classify (see List methods) is the higher-level grouping tool built on this idea.
%h.kv, %h.pairs, %h.keys, %h.values iterate a hash — see Hash methods.