Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!sun-barr!newstop!central!convex!usenet
From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: does perl have an "in" operator?
Message-ID: <1991May16.014446.10539@convex.com>
Date: 16 May 91 01:44:46 GMT
References: <RUSTY.91May14133645@groan.Berkeley.EDU>
Sender: usenet@convex.com (news access account)
Reply-To: tchrist@convex.COM (Tom Christiansen)
Distribution: comp
Organization: CONVEX Software Development, Richardson, TX
Lines: 47
Nntp-Posting-Host: pixel.convex.com

From the keyboard of rusty@groan.Berkeley.EDU (Rusty Wright):
:I've used a language where with arrays there's an "in" operator that
:checks to see if an element is in an arry.  For example, if you do
:
:	@array = ( 1, 2, 3 );
:
:	if ( 1 in @array ) { print "true\n"; }
:
:it would print true.  Does perl have anything like this?

Not as such.  Here's question #26 from the FAQ:

26) How can I test whether an array contains a certain element?

    There are several ways to approach this.  If you are going to make this
    query many times and the values are arbitrary strings, the fastest way is
    probably to invert the original array and keep an associative array around
    whose keys are the first array's values.

        @blues = ('turquoise', 'teal', 'lapis lazuli');
        undef %is_blue;
        grep ($is_blue{$_}++, @blues);

    Now you can check whether $is_blue{$some_color}.  It might have been a
    good idea to keep the blues all in an assoc array in the first place.

    If the values are all small integers, you could use a simple
    indexed array.  This kind of an array will take up less
    space:

        @primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31);
        undef @is_tiny_prime;
        grep($is_tiny_prime[$_]++, @primes);

    Now you check whether $is_tiny_prime[$some_number].

    If the values in question are integers, but instead of strings,
    you can save quite a lot of space by using bit strings instead:

        @articles = ( 1..10, 150..2000, 2017 );
        undef $read;
        grep (vec($read,$_,1) = 1, @articles);

    Now check whether vec($read,$n,1) is true for some $n.
--
Tom Christiansen		tchrist@convex.com	convex!tchrist
		"So much mail, so little time."