I'm surprised that returning a list of keys is faster than returning a hashref and then getting its keys. A dereference requires more operations, but should it be that much?
A good chunk of the time is spent in building the hash, so I added a baseline sub to measure it. I also reduced the number of iterations so it would run in reasonable time on my machine. And some minor formatting of results.
This is perl 5, version 28, subversion 0 (v5.28.0) built for MSWin32-x
+64-multi-thread
# Adapted from https://www.perlmonks.org/?node_id=11134740
use strict;
use warnings;
use Benchmark;
use Data::Dumper;
# Note: You can increment a string in Perl! WOW!
# As long as you don't use the string in a numeric context!
# $string++ is quite different than $string +=1
#
# Below, this is used to make a bunch of unique hash keys
# I don't think that the fact that they are sequential in
# an alphabetic sense makes much difference in the generated
# hash table because of the way that the Perl hash algorithm
# works.
sub baseline {
# create a large hash but return nothing
my $string = "ABCDEFGHIJ";
my %hash = map{$string++ => 1}(1..100000);
return;
}
sub return_hash
{
# create a large hash and return that entire hash as list
my $string = "ABCDEFGHIJ";
my %hash = map{$string++ => 1}(1..100000);
return %hash;
}
sub return_hash_ref
{
# create a large hash and return a ref to that hash
my $string = "ABCDEFGHIJ";
my %hash = map{$string++ => 1}(1..100000);
return \%hash;
}
sub return_just_keys
{
# create a large hash and return just the keys of that hash
my $string = "ABCDEFGHIJ";
my %hash = map{$string++ => 1}(1..100000);
return keys %hash;
}
timethese(200, {
'1)Keys of Hash via list ' => 'my @keys = keys %{{return_hash()}}
+',
'2)Keys of Local Hash copy' => 'my %hash2 = return_hash(); my @key
+s = keys %hash2;',
'3)Keys of local Hash Ref ' => 'my $href = return_hash_ref(); my @
+keys = keys %$href;',
'4)Just the returned keys ' => 'my @keys = return_just_keys()',
'5)Baseline ' => 'my $res = baseline()',
});
__END__
Benchmark: timing 200 iterations of 1)Keys of Hash via list , 2)Keys
+of Local Hash copy, 3)Keys of local Hash Ref , 4)Just the returned ke
+ys , 5)Baseline ...
1)Keys of Hash via list : 50 wallclock secs (49.44 usr + 1.52 sys =
+50.95 CPU) @ 3.93/s (n=200)
2)Keys of Local Hash copy: 50 wallclock secs (49.98 usr + 0.38 sys =
+50.36 CPU) @ 3.97/s (n=200)
3)Keys of local Hash Ref : 35 wallclock secs (34.75 usr + 0.34 sys =
+35.09 CPU) @ 5.70/s (n=200)
4)Just the returned keys : 33 wallclock secs (32.51 usr + 0.16 sys =
+32.67 CPU) @ 6.12/s (n=200)
5)Baseline : 25 wallclock secs (24.86 usr + 0.20 sys =
+25.06 CPU) @ 7.98/s (n=200)
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.