Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: uniq'ing arrays
Message-ID: <10501@jpl-devvax.JPL.NASA.GOV>
Date: 21 Nov 90 18:02:46 GMT
References: <1990Nov21.021344.16038@fxgrp.fx.com>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 25

In article <1990Nov21.021344.16038@fxgrp.fx.com> grady@postgres.berkeley.edu writes:
: grep is a useful unix utility that has a parallel perl operator.
: What about uniq?  I'd like to see uniq (or something) that strips
: out the duplicates in an array.  It would be cool if it were
: built into perl.
: 
: Meanwhile, has anyone written an efficient routine to do this?
: Linear time would be nice.  I'd like one that doesn't require the
: array to be sorted.  I could write one myself, but I thought
: I'd avoid duplicating code..

sub uniq {
    local(%seen);
    grep(!$seen{$_}++, @_);
}

@out = &uniq(@in);

It's more-or-less linear, apart from the extra time to bifurcate %seen
occasionally as it's growing.  I don't know whether you want to call it
efficient--it's going to depend on how quickly your machine can calculate
the hash function.  It may be faster to sort and compare adjacent values,
depending...

Larry