Beefy Boxes and Bandwidth Generously Provided by pair Networks
Syntactic Confectionery Delight

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

Here's uniq from List::MoreUtils:

sub uniq (@) { my %h; map { $h{$_}++ == 0 ? $_ : () } @_; }

I think this is equivalent to your "my %h; @uniq = grep { ! $h{$_}++ } @in;". What's important about both of them is that they don't do this:

sub bad_uniq { my %h; @h{@in} = (); return keys %h; }

...which may be more succinctly (idiomatically) written as "keys %{{ map { $_ => 1 } @in }}".

The difference is that keys will not return what was in the list to begin with but rather whatever those things come out as after being stringified. The solutions using map and grep both will stringify the stuff you feed them, but it's the stuff that's returned, and not the stringy leftovers that were used to tell which were duplicates.

Update with a demonstration:

use List::MoreUtils 'uniq'; use Data::Dumper; my $aref = [ 1, 2 ]; my @aref_duplicated = ( $aref, $aref, $aref ); my @u1 = uniq( @aref_duplicated ); my @u2 = keys %{{map {$_=>1} @aref_duplicated}}; print Data::Dumper->Dump( [ \@u1, \@u2 ], [ '*from_uniq', '*from_keys' ] ); __END__ @from_uniq = ( [ 1, 2 ] ); @from_keys = ( 'ARRAY(0x8153c28)' );

In reply to Re^3: Idiom: hashes as sets by kyle
in thread Idiom: hashes as sets by vrk

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others avoiding work at the Monastery: (6)
    As of 2017-11-25 00:15 GMT
    Find Nodes?
      Voting Booth?
      In order to be able to say "I know Perl", you must have:

      Results (354 votes). Check out past polls.