This module provides a number of list utility functions, all of which
take an initial code block to control their behaviour.  They are
variations on similar core perl or List::Util functions of similar
names, but which use the block to control their behaviour.  For
example, the core Perl function sort takes a list of values and
returns them, sorted into order by their string value.  The sort_by
function sorts them according to the string value returned by the
extra function, when given each value.

WWW: http://search.cpan.org/dist/List-UtilsBy/