in reply to Calculating the average of a column in a flat-file database

Greetings suggus,

Try this...

open(HANDLE,"script_integration_records");
while (<HANDLE>) {
    @temp1 = split(/:/);
    $domain = unpack ("A4", $temp1[40]);
    if (($domain eq "ATM") && ($temp1[36] eq "In Production")) {
        $sum += $temp1[38];
        $count++;
    }
}
close(HANDLE);

$average = $sum / $count;
print $average, "\n";

[download]

-gryphon
code('Perl') || die;

UPDATE:

Well, here's a smaller version of the above. I'm sure I could use map to get this in a line or two less, but I'm still having difficulties really getting my mind around complicated multi-calls of map. (Anyone out there know a tutorial on map?)

open(HANDLE, 'script_integration_records');
foreach (grep /^(?:[^:]*:){36}In Production:/, <HANDLE>) {
    my @line = split(/:/);
    push @numbers, $line[38] if (unpack("A4", $line[40]) eq "ATM");
}
close(HANDLE);

print eval(join('+',@numbers))/($#numbers+1), "\n";

[download]

Theoretically, you could run multiple greps against eachother to get just a single array. Then just average the array. Also, I have a general "ungood" feeling about using eval anywhere for any reason. Perhaps it's just a personal problem, but I have this fear of stuff being executed without my pre-knowledge of its contents.

-gryphon
code('Perl') || die;

Replies are listed 'Best First'.
Re: Re: Calculating the average of a column in a flat-file database
by Hofmator (Curate) on Oct 26, 2001 at 13:34 UTC

    Let me add a few comments and suggestions:

    • I would declare all variables with my, otherwise you might run into problems later - apart from the fact that it won't run under use strict.
    • You were looking for a map solution, here you go: 
      #!/usr/bin/perl
use strict;
use warnings;
 
# always check if open fails
open(DB, '<test.data') or die "Couldn't open file: $!";
my @numbers = map {
      my ($prod, $num, $dom) = (split /:/)[36,38,40];
      (unpack("A4",$dom) eq 'ATM' && $prod eq 'In Production')?$num:()
  } <DB>;
close DB;
 
my $sum;
$sum += $_ foreach (@numbers);
 
printf "The average is %.2f.", @numbers ? ($sum/@numbers) : 0;

      [download]
      I'm not saying that this is a better solution, I'd go - for the sake of readability/maintainability - for something straight forward like your first version.
    • Instead of the eval you can use a loop like I did or have a look at List::Utils.

    -- Hofmator

[reply]
[d/l]
Re: Re: Calculating the average of a column in a flat-file database
by suggus (Sexton) on Oct 26, 2001 at 02:58 UTC
    THANKS gryphon! It works! You rock!
[reply]

In Section Seekers of Perl Wisdom