Excellent solution. The interesting thing about Perl Golf is how different people tackle problems in terms of their favourite tools; map, sort, regex, grep, closures, slices or whatever.

Just for fun I ran your solutions through Perltidy as a test case. Here is the output: 
sub nn {
    my @x = @_[0, 1];
    @_ = sort {
        abs $x[0] - $x[1] < abs $a - $b or @x = ($a, $b);
        $a <=> $b;
    } @_;
    @x
}

sub nn {
    () = sort {
        abs $_[0] - $_[1] < abs $a - $b or @_ = ($a, $b);
        $a <=> $b;
    } @_;
    @_
}

[download]
John.
--


In reply to Re: Re (tilly) 1: (Golf) Nearest Neighbors by jmcnamara
in thread (Golf) Nearest Neighbors by MeowChow

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