Re: [MacPerl-AnyPerl] an elegant uniquing

[Ronald J Kimball <rjk@linguist.dartmouth.edu>]

On Sat, Feb 05, 2000 at 10:35:48PM -0500, Nathaniel Irons wrote:
> I've got an array full of anonymous hashes, each with 4-6 keys.  I would
> like to create a few arrays containing uniqued values from one of those
> keys, across all the hashes.
> 
> This is a neat one-line trick I got from the Cookbook:
> 
>  @unique = grep { ! $seen{ $_ }++ } @not_unique;
>   
> which I assumed I could adapt to my needs:
> 
>  @unique_names = grep { ! $seen{ ${$_}{names}++ } @array_of_hashes;

Unbalanced curly braces.  I think that should be:

@unique_names = grep { !$seen{ ${$_}{names} }++ } @array_of_hashes;


> which works, in that I get the right number of elements, but fails in
> that my new @u_names array is full of hash references, and not stringy
> hash values.  grep is returning "$_", not "${$_}{names}" as I intended.

grep always returns $_ for each match; that's what it's for.  grep selects
elements from the list that match the conditional expression.


> Is there a way to do this in one line?

What's so bad about two lines?

$seen{ ${$_}{names} }++ foreach @array_of_hashes;
@unqiue_names = keys %seen;


But here's one line:

@unique_names=map{!$seen{${$_}{names}}++?${$_}{names}:()}@array_of_hashes;


Ronald

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