Beware context. A quick test: 

  perl -MBenchmark=cmpthese -wle 'cmpthese(1, { context => q{print wan
+tarray ? "list" : defined(wantarray) ? "scalar" : "void"}})'

[download]
shows that these blocks are called in void context, and I believe that grep has optimisations in place for that. It would be worth assigning the results to an array to make sure you are actually benchmarking the right thing.

However I tried that here, and got similar results to you (the maximum difference being 10%), so I think you can discount permutations of the grep as a source of significant savings and concentrate on whichever version reads best to you.

In the context of the for loop, however, you may be better off losing the grep altogether - writing it as something like:

  for my $element (@array) {
    length($element) or next;
    ...
  }

[download]
would avoid the need to copy the list to the stack, which might well be a win for long lists.

Hugo

In reply to Re: Benchmarking the block and list forms of grep by hv
in thread Benchmarking the block and list forms of grep by grinder

Title:
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, details, 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, summary, 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.