Raku Books / Using Raku / Aggregate Data Types / Multi-dimensional data

68. Sort hashes by parameter

Sort a list of hashes using data in their values.

This task is commonly performed to sort items where the sortable parameter is one of the values in the hash, for example, sorting a list of people by age.

my @people = (
    {
        name => 'Kevin', age => 20,
    },
    . . .
    {
        name => 'Amanda', age => 19,
    },
);

@people.sort( *<age> ).say;

Using *<age> is the same as {%^a<age> <=> %^b<age>}.

The sort method uses an optional code block that customises the sorting procedure. It takes two arguments, compares them, and returns the result of the comparison.

In the example shown, %^a and %^b are the two placeholder variables created by the compiler. They alphabetically correspond to the first and the second arguments that the block receives.

Alternatively, it is possible to list the arguments in a pointy block explicitly:

@people.sort( -> %first, %second {
    %first<age> <=> %second<age>
}).say;

← 67. Transpose a matrix | 69. Count hash values →

68. Sort hashes by parameter

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