in reply to Finding Empty Columns

I am using the following code to try and determine if a column has any data other then 0

Ill assume you mean 0 or empty 

use strict;
use warnings;
use Data::Dumper;
my @rows;
my @empty;
while (<>) {
  chomp;
  my @row=split /;/;
  push @rows,\@row;
  $empty[$_]||=$row[$_] for 0..$#row;
}
print "Empty columns:",join(", ",grep { $empty[$_] } 0..$#empty),"\n";
print Data::Dumper->Dump([\@rows],['*rows']);

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HTH

---
demerphq


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Re: Re: Finding Empty Columns
by Anonymous Monk on Feb 14, 2003 at 21:01 UTC
    This seems to work, but can you explain to me what is actually going on ?

    Thanks

[reply]
      use strict;
use warnings;
use Data::Dumper;

my @rows;               # Store the rows here
my @empty;              # If we see a true value we put it here
while (<>) {            # read a line at a time
  chomp;                # lose the newline
  my @row=split /;/;    # split the line by ;
  push @rows,\@row;     # store the row 
  $empty[$_]||=$row[$_] # Equivelent to saying $empty[$_] or ($empty[$
+_]=$row[$_])
     for 0..$#row;      #   for each column
}
print "Empty columns:",join(", ",grep { $empty[$_] } 0..$#empty),"\n";
print Data::Dumper->Dump([\@rows],['*rows']);

      [download]

      I suppose @empty is a misnomer. It probably should be called @has_data and the code would be clearer. The basic idea is to maintain an array of flags, where the flag tells us if we have seen a value we care about. Since you said "0" this equates to FALSE (along with undef and "") so the ||= operator comes in. It basically says "unless the left side is TRUE, assign it the value on the right side". And since anything but the aformentioned values are true its an elegant way to set the flags.

      ---
      demerphq


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[d/l]

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