[Numpy-discussion] String sort

Francesc Altet faltet@carabos....
Fri Feb 8 11:31:15 CST 2008


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.

Cheers,

-- 
>0,0<   Francesc Altet     http://www.carabos.com/
V   V   Cárabos Coop. V.   Enjoy Data
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