harry34 has asked for the wisdom of the Perl Monks concerning the following question:

If I have the following output how would I code to output a list of duplicate data only (e.g A(01)in this case).
Needs to be coded in a general fashion as numbers and letters could change.

@array =

A(01)
B(02)
C(03)
A(01)
D(04)
E(05)

Thanks for your help Harry

Replies are listed 'Best First'.
Re: finding duplicate data
by gjb (Vicar) on Jan 21, 2004 at 10:49 UTC

    Sounds very much like homework, so I'll just give you a tip: a hash (e.g. %data) would come in handy. You can use the data (A(01), B(02), etc) as keys and the number of times you encounter the data as values. 

      $data{$line}++;

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    would do the trick.

    As a final step, you iterate over the keys (the function keys is useful here) in the hash and print those keys that have values larger than 1.

    Hope this helps, -gjb-

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Re: finding duplicate data
by borisz (Canon) on Jan 21, 2004 at 10:54 UTC
    use a hash to count the number of each string occurance. 
    #!/usr/bin/perl

while (<DATA>){
  chomp;
  $h{$_}++;  
}

for ( sort grep { $h{$_} != 1 } keys %h ) {
  print "$_\n";
}

__DATA__
A(01) 
B(02) 
C(03) 
A(01) 
D(04) 
E(05)

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    Boris
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      That works great !.
      What is the second part of the code doing ?
      i.e. how is it working ?
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        Which part has you puzzled? grep? for () implicitly setting $_? (If the former, you should be able to run "perldoc -f grep" to get a description of what grep does. If for some reason you have a broken perl that doesn't include perldoc, try here.)
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Re: finding duplicate data
by l3nz (Friar) on Jan 21, 2004 at 12:39 UTC
    This is an one-liner. As you can see, you can check the threshold value for items to show up by tuning the constant. Hope this helps. 

    map { print $_ if ( $h{$_}++ == 1) } <DATA>;

__DATA__
A(01) 
A(01) 
A(01) 
B(02) 
C(03) 
A(01) 
D(04) 
E(05) 
...

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    One-liners are definitely funny.
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Re: finding duplicate data
by chimni (Pilgrim) on Jan 21, 2004 at 11:50 UTC

    You could also do it in a compact command line manner
    To find only the duplicate enteries
    perl -ne 'print if $h{$_}++' filename
    To find unique data
    perl -ne 'print unless $h{$_}++' filename
    Of course , you could simply do cat filename | uniq at the shell prompt for the second case.
    HTH,
    chimni
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      Useless use of cat, and a misunderstanding of uniq (it only looks for duplicate adjacent lines). Instead, use 
      sort -u filename

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      to find unique data (though the perl solution would be doing less work, and would not scramble the line order).

      To list the duplicate entries only once, 

      perl -ne 'print if $h{$_}++ == 1' filename

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      The PerlMonk tr/// Advocate
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