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Perl code to remove duplicate lines from text file

Posted on 1998-10-10
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Last Modified: 2008-03-17
Ok, I need a quick Perl script that can take a sorted text file and remove duplicate lines and my brain is too fried to write this myself so I'm hoping someone can save me some time.

I have a text file (mailing list) which consists of two fields per line: <email> (space as delimiter) (person's name in parenthesis) - I need a routine to read the text file and remove duplicates in the first field.

I'll also award points if someone can give you a unix solution to this.

This needs to handle a 12,000+ line text file and be case insensitive (in determining dupes).
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Question by:wisdom042597
3 Comments
 
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Author Comment

by:wisdom042597
ID: 1205214
As a plus, it would be nice to reject any e-mail field which doesn't contain the '@' symbol.

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Expert Comment

by:ozo
ID: 1205215
perldoc perlfaq4
  How can I extract just the unique elements of an array?

            There are several possible ways, depending on whether
            the array is ordered and whether you wish to preserve
            the ordering.

    a) If @in is sorted, and you want @out to be sorted:
    (this assumes all true values in the array)
                    $prev = 'nonesuch';
                    @out = grep($_ ne $prev && ($prev = $_), @in);

                This is nice in that it doesn't use much extra
                memory, simulating uniq(1)'s behavior of removing
                only adjacent duplicates. It's less nice in that it
                won't work with false values like undef, 0, or "";
                "0 but true" is ok, though.

    b) If you don't know whether @in is sorted:
                    undef %saw;
                    @out = grep(!$saw{$_}++, @in);

    c) Like (b), but @in contains only small integers:
                    @out = grep(!$saw[$_]++, @in);

    d) A way to do (b) without any loops or greps:
                    undef %saw;
                    @saw{@in} = ();
                    @out = sort keys %saw;  # remove sort if undesired

    e) Like (d), but @in contains only small positive integers:
                    undef @ary;
                    @ary[@in] = @in;
                    @out = @ary;

  How can I get the unique keys from two hashes?

            First you extract the keys from the hashes into arrays,
            and then solve the uniquifying the array problem
            described above. For example:

                %seen = ();
                for $element (keys(%foo), keys(%bar)) {
                    $seen{$element}++;
                }
                @uniq = keys %seen;

            Or more succinctly:

                @uniq = keys %{{%foo,%bar}};

            Or if you really want to save space:

                %seen = ();
                while (defined ($key = each %foo)) {
                    $seen{$key}++;
                }
                while (defined ($key = each %bar)) {
                    $seen{$key}++;
                }
                @uniq = keys %seen;

0
 

Accepted Solution

by:
pcrutch earned 800 total points
ID: 1205216
Here's the unix solution..

 sort -fu -t' ' -k 0 -o <textfile> <textfile> | \
   grep '^\w+\@\w+ '

As for the perl, here is a solution for either unix or Win32:
----
# Read in each line from STDIN or filename on cmd line
while(<>) {
  chomp;
  # Push it onto the text array
  push(@text);
}

# Loop through the sorted text array
foreach $line (sort @text) {
  # Split the line into fields
  ($email,$name) = split(' ',$line);

  # email has embedded '@'?
  next if (! $email =~ /\@/);

  # @nodup will contain no-duplicate emails
  if (! @nodup =~ /$email/i) {
    print '$email $name\n';
    push(@nodup,$email);
  }
}
----
Note this will print the first email/name pair of duplicate fields.

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