Perhaps you'll allow me a little plug for Array::Compare.

#!/usr/bin/perl -w

use strict;
use Array::Compare;

my $cmp = Array::Compare->new;

my @array1 = ("q", "w", "e", "r", "t", "z");
my @array2 = ("q", "w", "e", "r", "t", "y");

my @diffs = $cmp->full_compare(\@array1, \@array2);

if (@diffs) {
  print "No matches for @array1[@diffs]\n";
} else {
  print "Arrays match\n";
}
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"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg

This is a faq, but here goes:

my @array1 = ("q", "w", "e", "r", "t", "z");
my @array2 = ("q", "w", "e", "r", "t", "y");

my %hash;
@hash{@array2} = () x @array2;
my @not_there = grep { ! exists $hash($_} } @array1;
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Update: This method's run time is O(NlogN) or therabouts, while your attempt is O(N**2). ++fruiture for spotting a thinko, corrected.

After Compline,
Zaxo

This method's run time is O(NlogN) or therabouts, while your attempt is O(N**2).

I think your method is actually O(N+M) as you iterate each array once and johnirl's is O(N*M) because he iterates one array for each element in the other.

The difference in array size might be significant. That is why I used two different variables: N and M.

Update: A short /msg exchange with Zaxo prompted me to point out that searches and updates on hashes are expected to be O(1). That is, assuming that the hash function is a good one for your data. I believe it is a reasonable assumption to make here.

-sauoq
"My two cents aren't worth a dime.";

Try using Perl, not C ;-)

my @array1 = qw/a b c d e f/;
my @array2 = qw/  b c d    /;
# you see: result must be a, e and f
my @in1notin2 = do {
    my %tmp = map {($_=>undef)} @array2;
    grep not exists $tmp{$_}, @array1
};
print "The elements @in1notin2 can be found in array 1, but not in arr
+ay 2\n";
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On the odds that you're not a student looking for a quick fix (because you've given no hints to the contrary, unfortunately), I'd suggest one word: "FAQ".

-- Randal L. Schwartz, Perl hacker

Hey Merlyn,
you're dead right I am a student but this isn't a college deadline. I'm finishing my work experience in a week and I am seriously running out of time to finish my work. I realise that the answer is a realativly simple one it's just that time is of the essence and I rather spend the time I have on more complex than trying to figure it out when there are gracious and knowledgable monks as yourself out there for the asking.

j o h n i r l .

 Sum day soon I'Il lern how 2 spelI (nad tYpe)

sub in_array{
    my $value = shift;
    my @array = @_;
    foreach $item (@array){
    if($value eq $item){
        return 1;
    }
    }

    return 0;
}


@array1 = ("q", "w", "e", "r", "t","z");
@array2 = ("q", "w", "e", "r", "t","y");

foreach $value (@array1){
    if(!in_array($value,@array2)){
    print "Value $value does not match any value in \@array2\n";
    }
}
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-- 
Joost       downtime n. The period during which a system
            is error-free and immune from user input.
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