Comments on: Please sir, write my code.

Question: Please sir, write my code.

Geo — Thu, 29 Apr 2004 17:01:00 -0800

Any MeFi perl/cgi programmers feel like writing a few lines of code?

I need to add a function to an existing script, which looks like a piece of cake if you know perl.

Given a $newstring and a file of records, each consisting of a count and a string delimited by a space:

201 this.thing
23 that.thing
14 someother.thing
...

I need a function to check whether $newstring already exists in the file. If so, increment the count. If not, add a new record to the file with a count of 1. Finally, sort the file in descending order by count.

Maybe 5 minutes for you. Learning perl first for me. If it would be easier with fixed length counts like 0000201, that is fine, too.

If this is inappropriate for Ask MeFi, my apologies. I'll take it over to answers.google.

By: whatnotever

whatnotever — Thu, 29 Apr 2004 17:51:55 -0800

#!/usr/bin/perl

# the input string - this just gets it from the command line
$newstring = $ARGV[0];

# temp variables
my $found = 0;
my @lines;

# open filename.txt for reading
open FILE, "<filename.txt";

# for each line in the file
while (<FILE>) {
     # on any line with a number, a space, and $newstring, increment the number, and remember that we found it
     if (s/^(\d+)(?=\s+$newstring)/$1 + 1/e) {$found = 1;}
     # add this line to our array of lines
     push @lines, $_;
}

close FILE;

# if we didn't find it, make the new line
if (!$found) {
     push @lines, "1 $newstring\n";
}

# sort the lines
@lines = sort {int($a) <=> int($b)} @lines;

# open the same file for writing
open FILE, ">filename.txt";
# write out each line to the file
for (@lines) {print FILE;}
close FILE;

By: thebabelfish

thebabelfish — Thu, 29 Apr 2004 17:57:33 -0800

You should change whatnotever's line s/^(\d+)(?=\s+$newstring)/$1 + 1/e to s/^(\d+)(?=\s+\Q$newstring\E)/$1 + 1/e so that regex metachars in $newstring don't mess up the regex.

In any case, next time you have a Perl question, take it on over to PerlMonks where they answer questions like this all the time.

By: cmonkey

cmonkey — Thu, 29 Apr 2004 18:04:07 -0800

Another way of doing it:

$file = "/tmp/infile"; #replace with your input file
$out = "/tmp/outfile";
$found = 0;

open (IN, $file);
open (OUT, ">$out");

while (<IN>) {
  if ($_ =~ /$newstring/) {
     $counter, $string) = split /\s/;
     $counter++;
     $found = 1;
     print OUT "$counter $string\n";temp
     } else {
     print OUT $_;
     }
}

if ($found != 1) { print OUT "1 $newstring\n"; }
close(IN);
close(OUT);
`mv $out $file`;

By: nicwolff

nicwolff — Thu, 29 Apr 2004 18:12:35 -0800

Fine, until one CGI process opens and reads the file, another reads and writes it, and then the first overwrites the second's changes... Try this (but I didn't test it!):

use Tie::File;
sub update_count {
  my $newstring = shift;
  tie( my @records, Tie::File => 'filename' )->flock;
  s/^(\d+)(?=\s+\Q$newstring\E)/$1 + 1/e for @records;
  push @records, "1 $newstring" unless $1;
  @records = sort @records;
}

By: Geo

Geo — Thu, 29 Apr 2004 18:23:10 -0800

This is great! I love this place. I don't know why perl seems so impenetrable to me.

And thanks for the link to PerlMonks. That would be the place.

I hope I can return the favor one day. Need any Delphi?

By: nicwolff

nicwolff — Thu, 29 Apr 2004 18:52:40 -0800

Whoops! You wanted descending order, so that last line should be

@records = reverse sort @records;

By: nicwolff

nicwolff — Thu, 29 Apr 2004 19:01:21 -0800

OK, I'm silly - reverse is slow and the default sort won't work - here's one I actually tested:

@records = sort { (split ' ', $b)[0] <> (split ' ', $a)[0] } @records;

By: nicwolff

nicwolff — Thu, 29 Apr 2004 19:03:08 -0800

D'oh, MeFi tagulated my flying saucer! It's:

@records = sort { (split ' ', $b)[0] <=> (split ' ', $a)[0] } @records;

By: costas

costas — Thu, 29 Apr 2004 21:35:14 -0800

OK, I just have to do the same in python:



#!env python

import sys



def firstsort(this, that):

   return cmp(this[0], that[0])



infile = open(sys.argv[2], 'r')

outfile = open(sys.argv[3], 'w')

inlines = infile.readlines()

outlines = []



for line in inlines:

   count = line.split(' ')[0]

   string = line.split(' ')[1]

   if newstring == string:

      count += 1

   outlines.append((count, string))



outlines.sort()

outlines.reverse()



for line in outlines:

   outfile.write("%s %s" % line)

This is maximized for readability; I hope it's less impenetrable than perl :-)

By: Geo

Geo — Fri, 30 Apr 2004 07:21:02 -0800

I'm tempted to post an APL version. I'm sure it could be done in one line.

The posts have been instructive. All I need to do now is figure out the strange error messages from my ISP.

Thanks everyone.