On Tue, Feb 17, 2009 at 12:39, Jim Gibson <jimsgib...@gmail.com> wrote:
snip
>> open(MAP,"file.map") || die;
>
> It is better to use lexical variables for file handles, say why the open
> fails if it does not succeed, and use the low-precedence 'or' instead of
> '||':
>
> open( my $map, "file.map") or die("Can't open file.map: $!");
snip
If you are using the low precedence or, you don't need the
parenthesis; and you should always use the three argument version of
open instead of the two argument version to avoid possible code
injection and weird filename attacks:
open my $map, "<", "file.map"
or die "could not open file.map: $!";
snip
>> if ($snp[0] =~ /Chromosome/) {next};
>
> The eq operator will be faster than a regular expression:
>
> if( $type eq 'Chromosome' ) {
snip
These are not equivalent statements (the regex is not anchored).
Also, avoid making statements about efficiency without a benchmark to
back it up. Regexes can be faster than string comparisons*.
snip
> close(OUT1) and die("Error writing to $out1: $!");
snip
That should be
close OUT1
or die "could not close OUT1: $!";
The close function returns true if "returning true only if IO buffers
are successfully flushed and closes the system file descriptor".
Since or uses short-circuit logic, if the first statement is true it
doesn't execute the second statement.
* and here is the benchmark and the code used to generate the benchmark:
equal:
0
regex:
0
string of length 1
Rate equal regex
equal 13435080/s -- -44%
regex 23842620/s 77% --
string of length 10
Rate equal regex
equal 20579528/s -- -5%
regex 21575636/s 5% --
string of length 100
Rate regex equal
regex 10922666/s -- -23%
equal 14277994/s 31% --
string of length 1000
Rate regex equal
regex 14448882/s -- -13%
equal 16657660/s 15% --
#!/usr/bin/perl
use strict;
use warnings;
use List::Util;
use Benchmark;
my $s = "foo";
my %subs = (
regex => sub {
return $s =~ /^Chromosome$/ ? 1 : 0;
},
equal => sub {
return $s eq "Chromosome" ? 1 : 0;
},
);
for my $sub (sort keys %subs) {
print "$sub:\n", $subs{$sub}->(), "\n";
}
for my $n (1, 10, 100, 1_000) {
$s = rstr($n);
print "string of length $n\n";
Benchmark::cmpthese(-1, \%subs);
}
sub rstr {
return join '', map { ("a" .. "z")[int rand 26] } 1 .. int rand shift
}
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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