Comparing two sets

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

I'm trying to find a better way of doing the below and only printing the %hash results only once.

so instead of getting:

Four,4,Miss
Four,4,Miss
Four,4,Miss
Three,3,Miss
Three,3,Miss
Three,3,Hit
Two,2,Miss
Two,2,Hit
Two,2,Miss
One,1,Hit
One,1,Miss
One,1,Miss
[download]

I would like:

One,1,Hit
Two,2,Hit
Three,3,Hit
Four,4,Miss
[download]

--------

use strict;
use warnings;

my %hash = ("One","1","Two","2","Three","3","Four","4");
my @lines = ("One", "Two", "Three");

foreach my $i (keys %hash)
{
    foreach my $n (@lines)
    {
        if ($i eq $n)
        {
            print "$i,", $hash{"$i"}, ",Hit\n";
        }
        else 
        {
            print "$i,", $hash{"$i"}, ",Miss\n";
        }
    }    
}
[download]

Comment on Comparing two sets Select or Download Code

Replies are listed 'Best First'.
Re: Comparing two sets by kennethk (Abbot) on May 20, 2010 at 13:53 UTC
You can do this by following the logic in a FAQ: How do I compute the difference of two arrays? How do I compute the intersection of two arrays?. Essentially, this creates a hash with keys that correspond to the entries of `@lines`. You can then use that hash to check if the entries existed: `#!/usr/bin/perl use strict; use warnings; my %hash = ("One","1","Two","2","Three","3","Four","4"); my @lines = ("One", "Two", "Three"); my %count; foreach my $element (@lines) { $count{$element}++; } foreach my $i (sort {$hash{$a} <=> $hash{$b}} keys %hash) { if (exists $count{$i}) { print "$i,$hash{$i},Hit\n"; } else { print "$i,$hash{$i},Miss\n"; } } __END__ One,1,Hit Two,2,Hit Three,3,Hit Four,4,Miss` [download] Your output lines are also much more complex than they need to be; see Quote and Quote like Operators. As well, you don't need to stringify to use something as a hash key - Perl does that automatically. Compare your output lines to the ones I have above.	[reply] [d/l] [select]
Re^2: Comparing two sets by Gizmo (Novice) on May 20, 2010 at 14:15 UTC
Thanks for the links. There's still a lot I need to learn.	[reply]
Re^3: Comparing two sets by Old_Gray_Bear (Bishop) on May 20, 2010 at 18:46 UTC
" ... There's still a lot I need to learn. " Don't feel alone; I have been playing with this language for 10+ years and I keep running across something new and wonderful every day. When I'm asked to rate my Perl knowledge during an interview, I say that "I am a 7.5 out of 10 -- I know the basics fairly well, and some of the more advanced topics; but I also know that there 30% of Perl that I've never used before. However, I do know where to go to read up on what I need to learn about what I don't know." This sometimes (quite often) segues into a discussion about "how do you know what you don't know" and completely derails the interviewer for half an hour or so. ---- I Go Back to Sleep, Now. OGB	[reply]
Re: Comparing two sets by JavaFan (Canon) on May 20, 2010 at 13:44 UTC
Untested: `my %lines = map {($_, 1)} qw [One Two Three]; my %hash = qw [One 1 Two 2 Three 3 Four 4]; foreach my $key (sort {$hash{$a} <=> $hash{$b}} keys %hash) { print "$key,", $hash{$key}; print $lines{$key} ? ",Hit\n" : ",Miss\n"; }` [download]	[reply] [d/l]