Perl module to select and sort top n elements of a list

 The functions available from this module select the top n elements from a
 list using several common orderings and custom key extraction procedures.
 .
 They are all variations around 'keytopsort { CALC_KEY($_) } $n => @data;'.
 .
 In array context, this function calculates the ordering key for every element
 in @data using the expression inside the block. Then it selects and orders
 the $n elements with the lower keys when compared lexicographically.
 .
 In scalar context, the value returned by the functions on this module is the
 cutoff value allowing to select nth element from the array.