Sorting is an O(n log n) operation, so the comparison sub gets called on average more than once for each element of the list being sorted. So if you have some sort of transformation to do to the data, you're going to be doing it multiple times for at least some of the elements if you include the transformation in the comparison sub.

If the transformation is expensive relative to building an arrayref and dereferencing it, the ST will give you gains in efficiency as the number of elements to be sorted increases, because you do the transformation exactly once per element.

Another way to get the do-it-only-once efficiency would be to Memoize (or cache the results from) the transformation function.

Caution: Contents may have been coded under pressure.

In reply to Re: When does it pay to use the schwartzian transform? by Roy Johnson
in thread When does it pay to use the schwartzian transform? by tphyahoo

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.