Finding duplicates within an array

[HughbertD]

Hi all,

I am writing a program, so far I have written the contents of the file (in this case filenames) into an array - now I want to find any duplicate filenames within the array and print them to another file - I am having a hard time getting my head around the logic to do this?

Can anyone help?

 

[feherke]

Hi

Brute force :

for ($i=0;$i<(scalar @a)-1;$i++) {
  for ($j=$i+1;$j<scalar@a;$j++) {
    print "$a[$i] duplicated at position $i and $j\n" if $a[$i] eq $a[$j];
  }
}

The same but deals nicer with multiple positions :

for ($i=0;$i<(scalar @a)-1;$i++) {
  $s="";
  for ($j=$i+1;$j<scalar@a;$j++) {
    $s.=($s?"":$i).", $j" if $a[$i] eq $a[$j];
  }
  print "$a[$i] at positions $s\n" if $s;
}

Feherke.

http://rootshell.be/~feherke/

 

[HughbertD]

Thank you for the reply -

@a is my array with filenames in?

 

[feherke]

Hi

Oops. I want to give it a nicer name, but finally I forgot it. Yes, it is the array with filenames.

Feherke.

http://rootshell.be/~feherke/

 

[ishnid]

Use a hash:

my %counter;
$counter{$_}++ for @filenames;

print "Duplicates\n";
for (keys $counter) {
   print "$_\n" if ( $counter{$_} > 1 );
}

 

[HughbertD]

Hi Ishnid -

I get this error - I know so little about hashes I'm not sure what it means

Type of arg 1 to keys must be hash (not scalar dereference) at add_file_map.pl line 35, near "$counter) "
Execution of add_file_map.pl aborted due to compilation errors.

 

[brigmar]

it's a typo:
the for() loop should read:

for (keys %counter) {

 

[HughbertD]

There must be a problem with the logic of the hash as it prints out each element of the array without duplication : where as I was hoping for every element of the array that had a duplicate

 

[HughbertD]

Ignore that post above - me being stupid - theres a problem in a loop earlier where I put the information into the array causing the array to have lots of duplicates for every entry -

Thanks for everyones help on this