[Numpy-discussion] String sort

Charles R Harris charlesr.harris@gmail....
Fri Feb 8 12:07:20 CST 2008


On Feb 8, 2008 10:31 AM, Francesc Altet <faltet@carabos.com> wrote:

> A Friday 08 February 2008, Francesc Altet escrigué:
> > A Friday 08 February 2008, Charles R Harris escrigué:
> > > > Also, in the context of my work in indexing, and because of the
> > > > slowness of the current implementation in NumPy, I've ended with
> > > > an implementation of the quicksort method for 1-D array strings.
> > > > For moderately large arrays, it is about 2.5x-3x faster than the
> > > > (supposedly) mergesort version in NumPy, not only due to the
> > > > quicksort, but also because I've implemented a couple of macros
> > > > for efficient string swapping and copy.  If this is of interest
> > > > for NumPy developers, tell me and I will provide the code.
> > >
> > > I have some code for this too and was going to merge it. Send yours
> > > along and I'll get to it this weekend.
> >
> > Ok, great.  I'm attaching it.  Tell me if you need some clarification
> > on the code.
>
> Ops.  I've introduced a last-minute problem in my code.  To fix this,
> just replace the flawed opt_strncmp() that I sent before by:
>
> static int inline opt_strncmp(char *a, char *b, int n) {
>  int i;
>  for (i=0; i<n; i++) {
>    if (a[i] > b[i]) return i+1;
>    if (a[i] < b[i]) return -(i+1);
>    /* Another way, but seems equivalent in speed, at least here */
> /*     if (a[i] != b[i]) */
> /*       return (((unsigned char *)a)[i] - ((unsigned char *)b)[i]); */
>  }
>  return 0;
> }
>
> Apparently, this version works just fine.
>

Did you find this significantly faster than strncmp? There is also a unicode
compare, do you have thoughts about that?

Chuck
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