Delete keys in hash if they exist in another hash

tgolf4fun has asked for the wisdom of the Perl Monks concerning the following question:

Hello, another newbie here.

I have been working on a script for 3 days and cannot get this last part to work. I have two hashes %hash and %end.
the keys of %end are in %hash.
I want to delete the keys in %hash if they exist in %end this way when I print %hash after the iteration, it will contain the key/value pairs I want.
I then assign the %hash to an array and print the array.
I've used this code which give me "Use of Uninitialized.." errors

foreach $k(keys %hash){delete ($hash{$k}) unless exists $end{$_};}
[download]

I've tried to write this every way I can imagine, nothing works. Please oh please someone help me so I can get some sleep.

2004-11-12 Edited by Arunbear: Changed title from '3 days of frustration', as per Monastery guidelines

Comment on Delete keys in hash if they exist in another hash Download Code

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Re: Delete keys in hash if they exist in another hash by davorg (Chancellor) on Nov 11, 2004 at 09:00 UTC
I may be misunderstanding you, but I think you just want: `delete @hash{keys %end};` [download] Here's a simple program that demonstrates it: `#!/usr/bin/perl use strict; use warnings; my %hash = (one => 1, two => 2, three => 3); my %end = (two => 2); delete @hash{keys %end}; print "$_ => $hash{$_}\n" for keys %hash;` [download] By the way, I've taken my specification from your post where you say "delete the keys in %hash if they exist in %end", rather than your code which seems to do the opposite. -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply] [d/l] [select]
Re^2: Delete keys in hash if they exist in another hash by tgolf4fun (Novice) on Nov 13, 2004 at 00:23 UTC
Your code showed me what I was doing wrong. I've fixed this and my script works fine now. I kept skipping past the section on hash slices, now I know I should have stopped to read it. Your print command was also a big help. Thanks for your wisedom and patience for a newbie trying to make it up the ranks. :-)	[reply]
Re: Delete keys in hash if they exist in another hash by inman (Curate) on Nov 11, 2004 at 08:57 UTC
Try: `foreach $k (keys %hash){ delete ($hash{$k}) unless exists $end{$k}; }` [download] You were using $_ as the key to %end. You have not set $_ in the code you posted so it is unlikely to have a value that you want. This should clear the error.	[reply] [d/l]
Re^2: Delete keys in hash if they exist in another hash by tachyon (Chancellor) on Nov 11, 2004 at 09:49 UTC
`s/unless/if/` to be pedantic, but the clue is right of course.	[reply] [d/l]
Re^2: Delete keys in hash if they exist in another hash by tgolf4fun (Novice) on Nov 13, 2004 at 00:20 UTC
Thanks so much, what do they say about hind sight, anyway this worked. I just never put $k in $end{}. I can sleep now, and only hope that someday I can gain enough knowledge to help someone as you have I.	[reply]