Gossamer Forum: General: Perl Programming: Hash Slice

Jun 21, 2002, 11:12 AM

Paul

Veteran (19537 posts)

Jun 21, 2002, 11:12 AM

Post #1 of 10

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Hash Slice

I've just had to use a hash slice for the first time ever...how exciting.

Code:
my @fields = $IN->param('fields'); 
my %slice; 

@slice{@fields} = map { [ 'some', 'stuff' ] } @fields;

It's pretty cool and helpful....strange it's taken me so long to actually use one.

Last edited by:

Paul: Jun 21, 2002, 11:13 AM

Jun 21, 2002, 10:04 PM

Ian

Veteran (2577 posts)

Jun 21, 2002, 10:04 PM

Post #2 of 10

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Re: [Paul] Hash Slice In reply to

Paul,

I have starred at this post for near 10 minutes now.... and I am no further forward in understanding it! Wink

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Jun 22, 2002, 12:02 AM

Aki

Staff / Moderator (429 posts)

Jun 22, 2002, 12:02 AM

Post #3 of 10

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Re: [Ian] Hash Slice In reply to

It's a neat little syntax trick.

The following two code snippets are equivalent.

Pretty basic:

Code:
%a = ( a => 'b', c => 'd' ); 
%b = ( e => 'f', g => 'h' ); 
$ populate b with values from a 
foreach my $key ( keys %a ) { 
  $b{$key} = $a{$key}; 
}

And Paul's way:

Code:
%a = ( a => 'b', c => 'd' ); 
%b = ( e => 'f', g => 'h' ); 
$ populate b with values from a 
@a{keys %b} = values %b;

And you've saved two lines of code! If you expect to redistribute your code, don't go crazy with it though, many people will have a hard time modifing all this perl xyzzy/job security stuff.

Jun 22, 2002, 12:09 AM

Ian

Veteran (2577 posts)

Jun 22, 2002, 12:09 AM

Post #4 of 10

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Re: [Aki] Hash Slice In reply to

Nice explanation!

Quote:

many people will have a hard time modifing all this perl xyzzy/job security stuff

Not to mention myself, when I forget what it all means again Wink

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Jun 22, 2002, 2:41 AM

Paul

Veteran (19537 posts)

Jun 22, 2002, 2:41 AM

Post #5 of 10

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Re: [Aki] Hash Slice In reply to

Code:
%a = ( a => 'b', c => 'd' );  
%b = ( e => 'f', g => 'h' );  
$ populate b with values from a  

foreach my $key ( keys %a ) {    
    $b{$key} = $a{$key};  
} 

-------------------------------------------------------------------------------- 


And Paul's way:  


-------------------------------------------------------------------------------- 
 Code  
-------------------------------------------------------------------------------- 


%a = ( a => 'b', c => 'd' );  
%b = ( e => 'f', g => 'h' );  
$ populate b with values from a  

@a{keys %b} = values %b;

Don't you have the hash slice back to front there?....it looks like it should be:

@b{keys %a} = values %a;

Otherwise the foreach loop is creating:

$b{a} = 'b'
$b{c} = 'd'

...and the hashslice creates:

$a{e} = 'f'
$a{g} = 'h'

Last edited by:

Paul: Jun 22, 2002, 2:43 AM

Jun 22, 2002, 10:11 AM

Aki

Staff / Moderator (429 posts)

Jun 22, 2002, 10:11 AM

Post #6 of 10

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Re: [Paul] Hash Slice In reply to

Aoch, ya got me. You're right! Hopefully I'll still get brownie points for the effort? Blush

Jun 22, 2002, 10:42 AM

Paul

Veteran (19537 posts)

Jun 22, 2002, 10:42 AM

Post #7 of 10

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Re: [Aki] Hash Slice In reply to

Definitely. You can have your "Helping the Community" badge too :)

Jul 23, 2002, 5:52 AM

Paul

Veteran (19537 posts)

Jul 23, 2002, 5:52 AM

Post #8 of 10

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Re: [Aki] Hash Slice In reply to

I'm starting to find more and more uses for hashslices now...for example with my plugin system, when uploading files a user may wish to delete some by ticking checkboxes so I can just do:

Code:
delete @$input{ map { "file_$_" } @bad };

Its so much easier than a foreach loop or something like that.

Jul 23, 2002, 9:58 AM

Aki

Staff / Moderator (429 posts)

Jul 23, 2002, 9:58 AM

Post #9 of 10

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Re: [Paul] Hash Slice In reply to

hehe, another idea: once in awhile i throw into my code a

Code:
  @$tags{ keys %$source } = values %$source;

but that's a bit confusing for code browsers in my opinion ;)

Last edited by:

Aki: Jul 23, 2002, 9:59 AM

Jul 23, 2002, 10:23 AM

Paul

Veteran (19537 posts)

Jul 23, 2002, 10:23 AM

Post #10 of 10

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Re: [Aki] Hash Slice In reply to

>>
but that's a bit confusing for code browsers
<<

All the better :)