NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/lang/perl/4854

Text File | 1992-07-21 | 3.2 KB | 87 lines

Newsgroups: comp.lang.perl
Path: sparky!uunet!centerline!noc.near.net!news.cs.brandeis.edu!chaos.cs.brandeis.edu!cos
From: [e-mail] (Ofer Inbar)
Subject: Re: easier way to determine set membership?
Message-ID: <[e-mail]>
Sender: [e-mail] (USENET News System)
Organization: Brandeis University
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>
Date: Tue, 21 Jul 1992 20:18:46 GMT
Lines: 75

[e-mail] (E. Tye McQueen) writes:
>Tom Christiansen <[e-mail]> writes:
>)From the keyboard of [e-mail] (E. Tye McQueen):
>):    @list =   ('bob', 'fred', 'joe', 'george');
>):    @group{@list} = (1) x @list;
>)
>)Um, yes, that's an exact quote from the posting of mine that
>)you quoted.  What's the difference?
>
>From memory your posting had the last line of:
>
>    @group{@list} = ();
>
>and a note about how this is a bit of a pain because you can't just
>check for "true".  My, admitedly slight, modification allows you
>to simply use $group{$element} as a boolean.

From TomC's original posting:
>Using as associative array is the right way to go for sets.
>A grep can pretty much always replace a for loop (except
>that you can't last out of it.)
>
>    grep ($group{$_}++,  'bob', 'fred', 'joe', 'george');
>    print "$x is ", ($group{$x} ? "" : "not "),  "a member\n";
>
>or
>
>    @list =   ('bob', 'fred', 'joe', 'george');
>    grep ($group{$_}++,  @list);
>    print "$x is ", ($group{$x} ? "" : "not "),  "a member\n";
>
>or
>    @list =   ('bob', 'fred', 'joe', 'george');
>    @group{@list} = (1) x @list;

Look at the last two lines above.  This is what Tom was referring to
when he said you made an exact quote from his posting.  You did :-)

And later on, from TomC's original posting:
>BTW, if you just want to make keys, you could do this:
>
>    @list =   ('bob', 'fred', 'joe', 'george');
>    @group{@list} = ();
>
>But then you can't really check $group{$member}, since its value will be
>undef.  But you can check it using keys() if you want.

Note the "if you just want to make keys."  Your correction to the
above section was actually a bug :-) since it took code meant to "just
make keys" and made it make keys *and* values instead.

Larry Wall then wrote:
>In article <[e-mail]> [e-mail] (Tom Christiansen) writes:
>: BTW, if you just want to make keys, you could do this:
>:
>:     @list =   ('bob', 'fred', 'joe', 'george');
>:     @group{@list} = ();
>:
>: But then you can't really check $group{$member}, since its value will be
>: undef.  But you can check it using keys() if you want.
>
>Or say
>
>    @group{@list} = (1) x @list;
>
>Larry

  Well, I guess if Larry can make the same mistake, that gives it a
measure of respectability, eh?  Guess you don't have to feel too bad
about it :-).  Aren't these misunderstandings fun!

  --  Cos (Ofer Inbar)  --  [e-mail]
  --  WBRS (BRiS)  --  [e-mail]  [e-mail]
  "Good literature is about Love and War."
  "Junk fiction is about Sex and Violence."