How to loop through file and count specific values in perl? - file

Question

Let's say I have a file with the lines such as:
*some numbers* :00: *somenumbers*
*somenumbers* :21: *somenumbers*
And for every number between :: I need to count how many times it repeats in the file?
while (<>){
chomp($_);
my ($nebitno,$bitno,$opetnebitno) = split /:/, $_;
$count{$bitno}++;
}
foreach $bitno(sort keys %count){
print $bitno," ",$count{bitno}, "\n";
}

Answer 1

What you produced was not bad code — it did the job for a single file at a time. Adapting the code shown in the question to handle multiple files, resetting the counts after each file:
#!/usr/bin/perl
use strict;
use warnings;
my %count = ();
while (<>) {
my ($nebitno, $bitno, $opetnebitno) = split /:/, $_;
$count{$bitno}++;
}
continue
{
if (eof) {
print "$ARGV:\n";
foreach $bitno (sort keys %count) {
print "$bitno $count{bitno}\n";
}
%count = ();
}
}
The key here is the continue block, and the if (eof) test. You can use close $ARGV in a continue block to reset $. (the line number) when the file changes; it is a common use for it. This sort of per-file summary is another use. The other changes are cosmetic. You don't need to chomp the line (though there's no particular harm done if you do); I print whole strings rather than using comma-separated lists (it works well here and very often). I use a few more spaces. I left it with the 1TBS format for the blocks of code, though I don't use that myself (I use Allman).
My draft solution used practically the same printing code as shown above, but the main while loop was slightly different:
#!/usr/bin/env perl
use strict;
use warnings;
my %counts = ();
while (<>)
{
$counts{$1}++ if (m/.*:(\d+):/);
}
continue
{
if (eof)
{
print "$ARGV:\n";
foreach my $number (sort { $a <=> $b } keys %counts)
{
print ":$number: $counts{$number}\n"
}
%counts = ();
}
}
The only advantage over what you used is that if some line doesn't contain a colon-surrounded number, it ignores the line, whereas yours doesn't consider that possibility. I'm not sure the comparison code in the sort is necessary — it ensures that the comparisons are numeric, though. If the numbers are all the same length and zero-padded on the left when necessary, there's no problem. If they're more generally formatted, the 'forced numeric' comparison might make a difference.
Remember: this is Perl, so TMTOWDTI (There's More Than One Way To Do It). Someone else might come up with a simpler solution.

Answer 2

Desired output can be achieved with following code snippet
look for pattern :\d+: in a line
increment hash %count for the digit
output result to console
use strict;
use warnings;
use feature 'say';
my %count;
/:(\d+):/ && $count{$1}++ for <>;
say "$_ = $count{$_}" for sort keys %count;