comparing lists and getting an exemtion report

Saadat.123 has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: comparing lists and getting an exemtion report by Riales (Hermit) on Apr 20, 2012 at 18:39 UTC
How big are these lists? If they're not incredibly large, something like this should work: `# Assuming @list_a and @list_b my %b; $b{$_} = 1 foreach (@list_b); my @list_c; foreach (@list_a) { push @list_c, $_ unless $b{$_}; }` [download]	[reply] [d/l]
Re^2: comparing lists and getting an exemtion report by brx (Pilgrim) on Apr 20, 2012 at 19:43 UTC
`# Assuming @list_a and @list_b my %b; $b{$_} = 1 foreach (@list_b); my @list_c = grep { not $b{$_} } @list_a;` [download]	[reply] [d/l]
Re: comparing lists and getting an exemtion report by Kenosis (Priest) on Apr 20, 2012 at 19:56 UTC
Although not as nicely readable as Riales's solution, here's another option: `map{$setB{$_}++}@listB; @listC = grep{!$setB{$_}}@listA;` [download] Hope this helps!	[reply] [d/l]
Re: comparing lists and getting an exemtion report by eyepopslikeamosquito (Archbishop) on Apr 21, 2012 at 00:37 UTC
Essentially the same question was asked today in removing a sublist. You might like to check the answers given there and perlfaq4 (arrays section) and Perl Cookbook, recipe 4.8 "Finding elements in one array but not another". Re performance, the way to find out is to use the Benchmark module to compare the running times of various solutions.	[reply]
Re: comparing lists and getting an exemtion report by BillKSmith (Monsignor) on Apr 21, 2012 at 01:41 UTC
The CPAN module List::Compare sounds perfect. I would certainly include it in any benchmark study of this problem. List::Compare	[reply]
Re^2: comparing lists and getting an exemtion report by AnomalousMonk (Archbishop) on Apr 21, 2012 at 01:52 UTC
A link to CPAN is often helpful: List::Compare.	[reply]
Re: comparing lists and getting an exemtion report by Anonymous Monk on Apr 20, 2012 at 21:37 UTC
I think that we would need to know a great deal more about the exact nature of your problem, and of your data and of where that data now is, in order to answer it meaningfully.	[reply]