The .classify method

    %addrbook.classify({ .value.substr(0,1).uc })

• .classify
• applies the block to each element
• returns a list of pairs where
• keys are the values returned from applying the block
• values are arrays of values that produced that key

Example:

my %hash = @list.classify( { $_ % 2 ?? 'odd' !! 'even' } );

say %hash<even>.perl;  # list of even elements in @list
say %hash<odd>.perl;   # list of odd elements in @list