Hashes

Key–value maps with the % sigil — look up with <...>, add pairs, test existence, iterate.

A hash maps keys to values and wears the % sigil. Build one from pairs (key => value) and look values up with <...>:

my %age = alice => 30, bob => 25;
say %age<alice>;
say %age<bob>;

30
25

For a key held in a variable, use curly braces instead: %age{$name}.

my %age = alice => 30, bob => 25;
my $who = 'bob';
say %age{$who};

25

Adding, testing, counting #

Assign to a new key to add it. The :exists adverb asks whether a key is present:

my %age = alice => 30;
%age<carol> = 28;
say %age.elems;
say %age<carol>:exists;
say %age<dave>:exists;

2
True
False

Iterating #

A hash has no fixed order, so sort before you print. Each element is a Pair with .key and .value:

my %population = tokyo => 37, delhi => 32, paris => 11;
for %population.sort -> $p {
    say "{$p.key}: {$p.value} million";
}

delhi: 32 million
paris: 11 million
tokyo: 37 million

Try it #

Count the letters of banana into a hash, then print the counts in sorted order. (Hint: 'banana'.comb gives the list of letters, and %count{$_}++ counts one.)

my %count;
for 'banana'.comb {
}

my %count;
for 'banana'.comb {
    %count{$_}++;
}
for %count.sort -> $p {
    say "{$p.key}: {$p.value}";
}

a: 3
b: 1
n: 2