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The following map variant works out significantly faster than the previously posted map variants, though not as fast as for-loop based variants:

sub variation3ep { my $idx = -1; my %hash = map(($_ => ++$idx), @array); }

While the block form of map is often favoured for its clarity, the expression form of map is faster because it avoids the overhead of creating a lexical pad.

This is actually another reason why BrowserUk's variation4 is fast - he uses the for statement modifier rather than a for loop with a block. Compare:

#!/usr/bin/env perl use strict; use warnings; use Benchmark qw(:all); my @array='aa' .. 'zz'; sub variation4 { my $idx = 0; my %hash; $hash{ $_ } = $idx++ for @array; } sub variation5 { my $idx = 0; my %hash; for (@array) { $hash{ $_ } = $idx++; } } cmpthese(-3, { 'variation4' => \&variation4, 'variation5' => \&variation5, }); __END__ Rate variation5 variation4 variation5 740/s -- -4% variation4 773/s 5% --

Yes, it's a small difference, but it's pretty consistently observable.

The absolute fastest I've been able to achieve is a small variation on BrowserUk's variation4 using the prefix increment rather than postfix increment:

sub variation6 { my $idx = -1; my %hash; $hash{ $_ } = ++$idx for @array; }

It seems to give you about a 6% speed up.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

In reply to Re^5: better array to hash conversion by tobyink
in thread better array to hash conversion by perltux

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