Zipped sorting

[Dmitry Olshansky]

On 25-Sep-12 06:18, bearophile wrote:
> This line of code sorts two arrays in "lock step", according to the
> items of the first array:
>
> zip(first, second).sort!q{a[0] < b[0]}();
>
> This code is handy, nice looking, short and sufficiently easy to
> recognize once you have seen it before.
>

Analyzing asm dump should help. But either way zip-sort heavily relies 
on proper inlining and I suspect it's not fully "unrolled".
Did you try DMD or other compilers?

> It's one case where D code is better than a Python version (and this
> returns two tuples instead of two lists):
>
> first, second = zip(*sorted(izip(first, second), key=itemgetter(0)))
>
> But with DMD on shortish arrays of about 20-30 items (each one 24 bytes
> long) I've seen that D code 3-5 times slower (to be sure of such timings
> I have to write down a proper benchmark) than sorting the items with
> simple manually written sorting D code, like a bubble sort or something
> similar (where inside swaps items of both arrays). So if this sorting is
> done in inner loops or critical parts of code, you can't use that
> zip+sort :-(
>
> Bye,
> bearophile


-- 
Dmitry Olshansky