Perl-Python-a-Day: Sorting

[Lasse Vågsæther Karlsen]

Xah Lee wrote:
> Sorting in Perl
> 
> In Perl, to sort a list, do like this:
> 
> @li=(1,9,2,3);
> @li2 = sort {$a <=> $b} @li;
> print join(' ', @li2);
> 
> 
> In Perl, sort is a function, not some Object Oriented thing. It returns
> the sorted result as another list. This is very simple and nice.

Like the sorted function in Python ?

li2 = sorted(li)

you can also specify a key and a cmp function if you need to.

<snip>
> In this way, the cost of the internals of the ordering function is
> avoided. (it runs on each list element once) However, your huge list is
> copied 1 extra time. So, there are pros and cons. Because this work
> around is very complex in both its semantics and syntax, it has
> acquired a coolness factor among Perl coders, and is given the name
> Schwartzian Transform.

That's about the worst explanation I've seen of Scwartzian Transform 
anywhere. Why deviate from what *every other source* does? Give an 
example, like the typical one of sorting filenames based on the size of 
the file they refer to. If you get the size in the comparison function, 
you can potentially get the size (which is a rather costly operation) 
many times for each file. Instead, you prefetch it once for each 
filename and store that in the list, and use the size as the key for 
sorting.

So while your explanation is technically correct, you lost some of the 
explaining factors. In other words, using Google lets anyone wanting to 
know about "Schwartzian Transform" find *much* better explanations than 
your mumbo jumbo.

But that's no surprise, you're Xah Lee anyway, loosing out is your 
middle name.

BTW, this way of doing the sort is nothing special for Perl, that 
construct can be seen many places simply because it does not fight any 
of Perls "problems" with sorting, instead it overcomes a common problem 
with sorting in any language.

> 
> It is interesting to note what compiler flaws can do to imperative
> languages and its people. In Python, the language syntax is tainted. In

tainted how?

> Perl, a complex construct is invented. In both camps, the basic

invented how?

> mathematics of sorting and its implementation aspects are completely
> belied.

belied how?

It's interesting to note that these "fact posts" of yours are nothing 
bud badly worded opinions.

-- 
Lasse Vågsæther Karlsen
http://usinglvkblog.blogspot.com/
mailto:lasse at vkarlsen.no
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