I have a Perl script that is counting the number of occurrences of various strings in a text file. I want to be able to check if a certain string is not yet a key in the hash. Is there a better way of doing this altogether?
Here is what I am doing:
foreach $line (@lines){
if(($line =~ m|my regex|) )
{
$string = $1;
if ($string is not a key in %strings) # "strings" is an associative array
{
$strings{$string} = 1;
}
else
{
$n = ($strings{$string});
$strings{$string} = $n +1;
}
}
}
I believe to check if a key exists in a hash you just do
if (exists $strings{$string}) {
...
} else {
...
}
print "foo exists now and you might not have expected that!" if(exists $test{'foo'}) - Drew 2015-09-15 13:52
I would counsel against using if ($hash{$key})
since it will not do what you expect if the key exists but its value is zero or empty.
Well, your whole code can be limited to:
foreach $line (@lines){
$strings{$1}++ if $line =~ m|my regex|;
}
If the value is not there, ++ operator will assume it to be 0 (and then increment to 1). If it is already there - it will simply be incremented.
I guess that this code should answer your question:
use strict;
use warnings;
my @keys = qw/one two three two/;
my %hash;
for my $key (@keys)
{
$hash{$key}++;
}
for my $key (keys %hash)
{
print "$key: ", $hash{$key}, "\n";
}
Output:
three: 1
one: 1
two: 2
The iteration can be simplified to:
$hash{$_}++ for (@keys);
(See $_
in perlvar.) And you can even write something like this:
$hash{$_}++ or print "Found new value: $_.\n" for (@keys);
Which reports each key the first time it’s found.
You can just go with:
if(!$strings{$string}) ....
$a{$x}{$y}
will create $a{$x}
, regardless if you use exists
or any other approach - rustyx 2016-05-23 14:57