Mode

sub mode (*@a) {
    my %counts := @a.Bag;
    my $max = %counts.values.max;
    %counts.grep(*.value == $max).map(*.key);
}

# Testing with arrays:
say mode [1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17];
say mode [1, 1, 2, 4, 4];

Output:

6
(4 1)

Alternatively, a version that uses a single method chain with no temporary variables: (Same output with same input)

sub mode (*@a) {
    @a.Bag                # count elements
      .classify(*.value)  # group elements with the same count
      .max(*.key)         # get group with the highest count
      .value.map(*.key);  # get elements in the group
}

say mode [1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17];
say mode [1, 1, 2, 4, 4];