help with a function that will cut out redundancy across two lists

annakarenina83 has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I'm a humble biologist who has just started to learn Perl (using Sam's 21 days book - I'm only on day seven!) and I need some help with a specific aspect of a script I'm trying to write (just a push in the right direction will do)

Briefly - I need to take two txt files, each with a list of names. There is some redundancy across these two lists (i.e some names appear in both lists) and that is the problem. I need to extract the names from both files (I think I know how to do this - I was just going to put the list of names from each file into two arrays, respectively)and then compare the elements of the arrays and somehow then output a file where it lists each name from both arrays only once (i.e remove the redundancy where a given name appears in both files). The part I need help with is which function/s I could use to only list the names that appear in both lists once (and also include the names that appear in only one of the lists). I hope that was clear.

Any help or a hint would be greatly appreciated. Cheers, Anna

Comment on help with a function that will cut out redundancy across two lists

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Re: help with a function that will cut out redundancy across two lists by wind (Priest) on May 20, 2011 at 05:11 UTC
The following resource hopefully will inspire what you need: perldoc - perlfaq4: How do I compute the difference of two arrays? How do I compute the intersection of two arrays?	[reply]
Re: help with a function that will cut out redundancy across two lists by Utilitarian (Vicar) on May 20, 2011 at 05:34 UTC
Hi Anna, Any time you need to remove duplicates in Perl think of using a hash and iterating over the two files incrementing a value indexed by the elements you're cleaning. If subsequently you need to find out how many instances of each element there was the associated value will tell you. Give this a go and if you have any problems get back to us. `print "Good ",qw(night morning afternoon evening)[(localtime)[2]/6]," fellow monks."`	[reply] [d/l]
Re: help with a function that will cut out redundancy across two lists by ww (Archbishop) on May 20, 2011 at 11:34 UTC
I can't speak to the quality of the Sams Learn Perl in 21 Days today, but if it's as it was about a decade ago, these suggestions may be helpful: Check the on-line errata when the material 'taught' before an exercise or problem "just doesn't work." Recheck against a reliable text (the newest edition of Learning Perl, O'Reilly, for instance). expand your library. recycle 21 Days.	[reply]
Re: help with a function that will cut out redundancy across two lists by dorko (Prior) on May 20, 2011 at 13:48 UTC
List::Compare does that and more: `use List::Compare; use Data::Dumper; @Llist = qw(abel abel baker camera delta edward fargo golfer); @Rlist = qw(baker camera delta delta edward fargo golfer hilton); $lc = List::Compare->new(\@Llist, \@Rlist); #Get those items which appear at least once in both lists (their inter +section). @intersection = $lc->get_intersection; print Dumper \@intersection;` [download] Cheers, Brent -- Yeah, I'm a Delt.	[reply] [d/l]
Re: help with a function that will cut out redundancy across two lists by Plankton (Vicar) on May 20, 2011 at 07:00 UTC
I think you want to do something like this ... `plankton@ubuntu:~$ cat seen.pl #!/usr/bin/perl -w use strict; my %seen; while(<>) { chomp; $seen{$_}++; } for my $name ( keys %seen ) { print "$name\n"; } plankton@ubuntu:~$ cat names1 delbert james t kirk lisa simpson george of the jungle molly plankton@ubuntu:~$ cat names2 adolf albert molly fortran plankton@ubuntu:~$ ./seen.pl names1 names2 albert molly james t kirk george of the jungle adolf delbert lisa simpson fortran` [download] ... right?	[reply] [d/l]