Match string in array

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

I have two lists of files. File list A is a list of files that have been transferred. File list B is a list of all files in a given directory. What I want to find is an item from list B that does not exist anywhere in list A. I just can't quite get my head around how to approach the problem.

@rray1=('one','red','orange','brown','green','blue','scarlett','fourte
+en');
@rray2=('red','orange','yellow','green','blue','indigo','violet');

foreach my $check (<@rray1>) {
        foreach my $item (<@rray2>) {
                if ($check ne $item) { 
                    <do something>
                }       
}#close foreach
[download]

The problem with this approach is pretty obvious: 'one' does not match anything in the second list, which would be what I want. However, 'red' matches 'red' but also shows as not matched on everything else. Basically, I think what I want is to find a string wherever it is in an array. I've tried playing with hashes (also grep) on this to see if the solution might be in that direction, but I'm at a loss as to where to go from here. I just need a prod in the right direction, not a full-blown solution.

thanks

Comment on Match string in array Download Code

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Re: Match string in array by JediWizard (Deacon) on Oct 03, 2005 at 19:10 UTC
`my(%listA) =(); @listA{'one','red','orange','brown','green','blue','scarlett','fourte +en'} = (); my(@listB) = ('red','orange','yellow','green','blue','indigo','violet' +); foreach my $check (@listB){ print "$check\n" if(! exists($listA{$check})); } __END__ # Output: yellow indigo violet` [download] They say that time changes things, but you actually have to change them yourself. —Andy Warhol	[reply] [d/l]
Re^2: Match string in array by nimdokk (Vicar) on Oct 03, 2005 at 19:29 UTC
++ Thanks, thats exactly what I needed.	[reply]
Re: Match string in array by ikegami (Patriarch) on Oct 03, 2005 at 19:46 UTC
Since noone mentioned it so far, `foreach my $check (<@rray1>) {` is very dangerous and inefficient. You should use `foreach my $check (@rray1) {` instead. `<@rray1>` is equivalent to `glob(join($", @rray1))` It is dangerous because a number of characters are special to `glob` (including spaces).	[reply] [d/l] [select]
Re: Match string in array by Skeeve (Parson) on Oct 03, 2005 at 19:54 UTC
`my(@rray1)=('one','red','orange','brown','green','blue','scarlett','fo +urteen'); my(@rray2)=('red','orange','yellow','green','blue','indigo','violet'); # If I got something like this, I usually do it this way: # 1. Make a hash out of the array you want to check: my (%hash); @hash{@rray1}= (); # 2. Delete everything from that hash that's in @rray2 delete @hash{@rray2}; # 3. What's left over is what you're searching print join("\n", keys %hash),"\n";` [download] `$\=~s;s.;q^\|D9JYJ^^qq^\//\\\///^;ex;print`	[reply] [d/l] [select]
Re: Match string in array by chester (Hermit) on Oct 03, 2005 at 19:15 UTC
The easy way... `use warnings; use strict; use Set::Array; my $array1 = Set::Array->new('one','red','orange','brown','green','blu +e','scarlett','fourteen'); my $array2 = Set::Array->new('red','orange','yellow','green','blue','i +ndigo','violet'); print "In array1, not in array2:\n"; print join "\n", $array1->difference($array2), "\n"; print "In array2, not in array1:\n"; print join "\n", $array2->difference($array1), "\n";` [download] Output: `In array1, not in array2: fourteen one brown scarlett In array2, not in array1: violet indigo yellow` [download]	[reply] [d/l] [select]
Re: Match string in array by polypompholyx (Chaplain) on Oct 03, 2005 at 19:09 UTC
You probably want something like this: use a hash to record all the items in the first array, then `grep` for items in the second array that you haven't already seen: `my %seen_in_1; $seen_in_1{$_}++ for @rray1; my @in_2_but_not_1 = grep { not $seen_in_1{$_} } @rray2;` [download] Or, to avoid duplicates: `my %seen_in_1; $seen_in_1{$_}++ for @rray1; my $seen_in_2_but_not_1; $seen_in_2_but_not_1{$_}++ for grep { not $seen_in_1{$_} } @rray2; my @in_2_but_not_1 = keys %seen_in_2_but_not_1;` [download]	[reply] [d/l] [select]
Re: Match string in array by gasho (Beadle) on Oct 03, 2005 at 19:09 UTC
`@FirstArray=qw(A B C D); @SecondArray=qw(D E F B); foreach $pr (@FirstArray){ #print "Property: $pr\n"; @match=(); @match=grep(/$pr/,@SecondArray); if (!@match){ push(@UniqueInFirstArrayNotFoundInSecondArray,$pr); } else { push(@FoundInBothArrays,$pr); } } print "".join("\n",@UniqueInFirstArrayNotFoundInSecondArray)."\n"; print "".join("\n",@FoundInBothArrays)."\n";` [download]	[reply] [d/l]
Re^2: Match string in array by sauoq (Abbot) on Oct 03, 2005 at 19:18 UTC
Everytime you use `grep`, you are iterating through the list. Since you do that inside of loop, your algorithm is O(N*M). In contrast, JediWizard iterates once through a loop so his algorithm is linear. His approach is also conceptually simpler which results in cleaner code. -sauoq "My two cents aren't worth a dime.";	[reply] [d/l]
Re: Match string in array by Hue-Bond (Priest) on Oct 04, 2005 at 20:28 UTC
Here's my try: `my @rray1=('one','red','orange','brown','green','blue','scarlett','fou +rteen'); my @rray2=('red','orange','yellow','green','blue','indigo','violet'); my @resul=grep { my $c=$_; grep /^$c$/, @rray1 } @rray2;` [download] This searches in `@rray1` every element in `@rray2`. So, what you want is simply the inverse: `my @resul=grep { my $c=$_; !grep /^$c$/, @rray1 } @rray2;` -- David Serrano	[reply] [d/l] [select]