Re: How can I find the index of the biggest element in an array?

[reisinge]

A one-liner where the array elements are the command line arguments:

$ perl -E 'say [ sort { $ARGV[$b] <=> $ARGV[$a] } 0..$#ARGV ]->[0]' 42
+ 1000 999 0 -1

[reisinge]

I was wondering about the efficiency of this solution so I compared it with GrandFather's solution:

# x.pl
use Benchmark qw(timethese cmpthese);

cmpthese(
    -2,
    {
        GrandFather => sub {
            my $idxMax = 0;
            $ARGV[$idxMax] > $ARGV[$_] or $idxMax = $_ for 1 .. $#ARGV
+;
            $idxMax;
        },
        reisinge => sub {
            [ sort { $ARGV[$b] <=> $ARGV[$a] } 0..$#ARGV ]->[0];
        }
    }
);

These are the results of the benchmarking:

$ perl x.pl $(seq 1 1000)
              Rate    reisinge GrandFather
reisinge    3742/s          --         -3%
GrandFather 3864/s          3%          --
$ perl x.pl $(seq 1 10000)
             Rate    reisinge GrandFather
reisinge    377/s          --         -5%
GrandFather 395/s          5%          --
$ perl x.pl $(seq 1 100000)
              Rate    reisinge GrandFather
reisinge    34.1/s          --        -18%
GrandFather 41.6/s         22%          --

GrandFathers's solution seems to be more efficient, i.e. it's faster (to run) and scales better. But mine is shorter :-).

[marioroy]

GrandFather's solution may be shorten if a short one-liner is what you're after.

# reisinge
perl -E 'say [ sort { $ARGV[$b] <=> $ARGV[$a] } 0..$#ARGV ]->[0]' 42 1
+000 999 0 -1

# GrandFather
perl -E '$m=0; $ARGV[$m] > $ARGV[$_] or $m=$_ for 1..$#ARGV; say $m' 4
[phone]

# Shorten, similar performance
perl -E '$i=0; ($ARGV[$m] > $_ or $m=$i), $i++ for @ARGV; say $m' 42 1
+000 999 0 -1

Below, please find a benchmark script for testing against a large list.

use strict;
use warnings;
use List::Util 'shuffle';
use Time::HiRes 'time';

# Return index to biggest element.

sub reisinge {
    [ sort { $_[$b] <=> $_[$a] } 0 .. $#_ ]->[0];
}

sub GrandFather {
    my $idxMax = 0;
    $_[$idxMax] > $_[$_] or $idxMax = $_ for 1 .. $#_;
    $idxMax;
}

sub biggest_elm {
    my ($idxMax,$idx) = (0,0);
    ($_[$idxMax] > $_ or $idxMax = $idx), $idx++ for @_;
    $idxMax;
}

srand 0;

my @list = shuffle 1..4e5;

for my $code (qw( reisinge GrandFather biggest_elm )) {
    no strict 'refs';
    my ($start, $idx) = (time, $code->(@list));

    printf "Index %d, Seconds (%-11s): %0.03f\n",
        $idx, $code, time - $start;
}

Regards, Mario.

Edit: Added benchmark script.

[reisinge]

Thanks Mario! Yeah, my solution doesn't scale well at all:

# Your benchmark script
Index 234638, Seconds (reisinge   ): 1.919
Index 234638, Seconds (GrandFather): 0.073
Index 234638, Seconds (biggest_elm): 0.072

# Your benchmark script =~ s/1\.\.4e5/1..4e6/;
Index 3167631, Seconds (reisinge   ): 33.464
Index 3167631, Seconds (GrandFather): 0.876
Index 3167631, Seconds (biggest_elm): 0.775