Editing Schwartzian transform (section)

==Efficiency analysis==
Without the Schwartzian transform, the sorting in the example above would be written in Perl like this:
<syntaxhighlight lang="perl">
@sorted = sort { foo($a) cmp foo($b) } @unsorted;
</syntaxhighlight>

While it is shorter to code, the naive approach here could be much less efficient if the key function (called {{mono|foo}} in the example above) is expensive to compute. This is because the code inside the brackets is evaluated each time two elements need to be compared. An optimal [[comparison sort]] performs ''[[big o notation|O]]''(''n log n'') comparisons (where ''n'' is the length of the list), with 2 calls to {{mono|foo}} every comparison, resulting in ''O''(''n log n'') calls to {{mono|foo}}. In comparison, using the Schwartzian transform, we only make 1 call to {{mono|foo}} per element, at the beginning {{mono|map}} stage, for a total of ''n'' calls to {{mono|foo}}.

However, if the function {{mono|foo}} is relatively simple, then the extra overhead of the Schwartzian transform may be unwarranted.