Re: Read file line by line and check equal lines

I thought I would tempt you with this version.

#!/usr/bin/perl

use strict;
use warnings;

my $previous;

&unique while(<DATA>);

sub unique
{
  return if $previous and $previous eq $_;
  print;
  $previous = $_;
}

__DATA__
a1a
a1a
b1b
c1c
c1c
d1d
d1d
e1e
f1f
g1g
g1g
h1h
h1h
i1i
j1j
k1k
k1k
k1k
[download]

-=( Graq )=-

Comment on Re: Read file line by line and check equal lines Download Code

Replies are listed 'Best First'.
Re^2: Read file line by line and check equal lines by Anno (Deacon) on Mar 06, 2007 at 13:07 UTC
Why the sub call with a leading ampersand (`&unique`)? Since perl 5 that form is no longer necessary and has the side-effect of using (and exposing)the caller's `@_` instead of building its own. You are not using `@_` at all, so it's unnecessary. Instead, your sub uses two global variavles, one lexical ($previous) and the package variable $_. That should be avoided except in very special cases. In this case it is hard to see why you use a sub at all. Just expand the code in the loop body. That would be clearer. Anno	[reply] [d/l] [select]
Re^2: Read file line by line and check equal lines by duff (Parson) on Mar 06, 2007 at 17:27 UTC
That doesn't exactly solve the stated problem, does it? As I read it, the OP only wants those lines that only appear one time in the input. What you've given is a way to display a given line from the input at most one time. Here's a solution (untested, so there's probably boundary problems) that only needs to keep at most 3 lines in memory under the constraint that the lines are already sorted. `#!/usr/bin/perl use strict; use warnings; my ($p1, $p2); while(<DATA>) { next unless $p1 and $p2; if ($p2 eq $p1) {$p2 = $p1 = undef; redo; } if ($p2 ne $p1) { print $p2; next; } } continue { $p2 = $p1; $p1 = $_; } __DATA__ a1a a1a b1b c1c c1c d1d d1d e1e f1f g1g g1g h1h h1h i1i j1j k1k k1k k1k` [download] duff	[reply] [d/l]


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