📘 Finding unique elements using Raku

Print all unique elements of the given array.

In Perl 6, objects of the Array type have the unique method.

my @a = 2, 3, 7, 4, 5, 5, 6, 2, 10, 7;
say @a.unique;

The result of running this program is a sequence containing the unique elements: (2 3 7 4 5 6 10).

Notice that the values are not sorted and appear in the same order as they first appeared in the original data, which stays unchanged.

The routine can be used as a function:

say unique(@a);

It can also take a code block or a reference passed via the with named argument to replace the default comparison method. The following example demonstrates how to select rational numbers that only repeat once within the given integer part.

<1.1 1.3 2.2 2.5 3.6>.unique(with => {
    $^a.Int == $^b.Int;
}).say;

From the given list of numbers, only three pass the filter: (1.1 2.2 3.6).

The $^a and $^b are the placeholder variables that receive pairs of values when the with code block is activated. Alternatively, arguments with explicit names may be used:

unique(@data, with => -> $x, $y {$x.Int == $y.Int}).say;