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Groups > comp.lang.perl.misc > #8844

Re: No more than N element of an array

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Quoth tmcd@panix.com:
> A cow-orker is coding something: he gets an array of results, but
> wants to take no more than the first 1000 elements.  His suggestion was
> 
> @results = @results[0 .. (MAXSEARCHRESULTS - 1,
> $#results)[MAXSEARCHRESULTS - 1 > $#results ]];
> 
> He felt it was "awesome".  I thought it was way too cute.

I'm not sure 'cute' is the word I'd use...

> Of course there's
> @results = @results[0 .. (MAXSEARCHRESULTS - 1 > $#results ? $#results :
> MAXSEARCHRESULTS - 1)];
> It has the same number of uses of variables, just in a different order.
> 
> I considered plain @results[0 .. MAXSEARCHRESULTS].  It works if the
> array is longer than the limit, but pads with undef if shorter:
> 
> $ perl -e 'use strict; use warnings; my @a = (0, 1, 2, 3, 4, 5, 6); @a =
> @a[0..10]; print join(",", @a), "\n"'
> Use of uninitialized value $a[7] in join or string at -e line 1.
> Use of uninitialized value $a[8] in join or string at -e line 1.
> Use of uninitialized value $a[9] in join or string at -e line 1.
> Use of uninitialized value $a[10] in join or string at -e line 1.
> 0,1,2,3,4,5,6,,,,
> 
> I thought of splice.
> 
> $ perl -e 'use strict; use warnings; my @a = (0, 1, 2, 3, 4, 5, 6);
> splice @a, 3; print join(",", @a), "\n"'
> 0,1,2
> $ perl -e 'use strict; use warnings; my @a = (0, 1, 2, 3, 4, 5, 6);
> splice @a, 10; print join(",", @a), "\n"'
> splice() offset past end of array at -e line 1.

You can kill this warning with

    no warnings "misc";

> 0,1,2,3,4,5,6
> $ perl -e 'print $], "\n"'
> 5.014002
> 
> But that's on my ISP.  On our office machines, no warning.
> 
> $  perl -e 'use strict; use warnings; my @a = (0, 1, 2, 3, 4, 5, 6);
> splice @a, 3; print join(",", @a), "\n"'
> 0,1,2
> $  perl -e 'use strict; use warnings; my @a = (0, 1, 2, 3, 4, 5, 6);
> splice @a, 10; print join(",", @a), "\n"'
> 0,1,2,3,4,5,6
> $  perl -e 'print $], "\n"'
> 5.016002
> $ perlfunc splice | cat
> ...
> If OFFSET is past the end of the array,
> Perl issues a warning, and splices at the end of the array.
> ...
> So is splice likely to ever output such a warning again, so the 5.16
> documentation is simply outdated?  Or was that just an error in 5.16
> and the warning now comes out in 5.18?

The behaviour changed in 5.16. In 5.14 and before, both these cases
warned:

    splice @a, 10, 3;
    splice @a, 10;

but for 5.16 it was decided that the second was actually entirely
unambiguous, so only the first case warns.

> To protect against that,
> splice @results, MAXSEARCHRESULTS if @results > MAXSEARCHRESULTS;
> Doable (warning: that's untested code).  But it's not as pretty.
> 
> Is there a cleaner way?

Perhaps

    @results = splice @results, 0, MAXSEARCHRESULTS;

Ben

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Thread

No more than N element of an array tmcd@panix.com (Tim McDaniel) - 2013-07-25 15:29 +0000
  Re: No more than N element of an array Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-25 16:38 +0100
    Re: No more than N element of an array Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-25 16:44 +0100
  Re: No more than N element of an array Ben Morrow <ben@morrow.me.uk> - 2013-07-26 05:12 +0100
    Re: No more than N element of an array Charles DeRykus <derykus@gmail.com> - 2013-07-25 23:08 -0700
      Re: No more than N element of an array Ben Morrow <ben@morrow.me.uk> - 2013-07-26 09:00 +0100
        Re: No more than N element of an array Charles DeRykus <derykus@gmail.com> - 2013-07-26 02:19 -0700
          Re: No more than N element of an array "Peter J. Holzer" <hjp-usenet3@hjp.at> - 2013-07-26 11:32 +0200
            Re: No more than N element of an array Charles DeRykus <derykus@gmail.com> - 2013-07-26 03:38 -0700
          Re: No more than N element of an array Ben Morrow <ben@morrow.me.uk> - 2013-07-26 11:26 +0100
          Re: No more than N element of an array tmcd@panix.com (Tim McDaniel) - 2013-07-26 14:27 +0000
            min (), and Perl modules Ivan Shmakov <oneingray@gmail.com> - 2013-07-26 15:16 +0000
              Re: min (), and Perl modules tmcd@panix.com (Tim McDaniel) - 2013-07-26 16:17 +0000
            Re: No more than N element of an array Ben Morrow <ben@morrow.me.uk> - 2013-07-26 16:39 +0100
        Re: No more than N element of an array Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-26 16:38 +0100
          Re: No more than N element of an array Ben Morrow <ben@morrow.me.uk> - 2013-07-26 19:23 +0100
            Re: No more than N element of an array Rainer Weikusat <rweikusat@mssgmbh.com> - 2013-07-30 17:52 +0100
              Re: No more than N element of an array Charles DeRykus <derykus@gmail.com> - 2013-07-30 22:10 -0700

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