[Numpy-discussion] Slow performance in array protocol with string arrays

[Francesc Altet]

Hi,

Perhaps this is not very important because it only has effects at high
dimensionality, but I think it would be good to send it here for the
records.

It seems that numarray implementation for the array protocol in string
arrays is very slow for dimensionality > 10:

In [258]: a=scicore.reshape(scicore.array((1,)), (1,)*15)

In [259]: a
Out[259]: array([[[[[[[[[[[[[[[1]]]]]]]]]]]]]]])

In [260]: t1=time(); c=numarray.array(a);print time()-t1
0.000355958938599   # numerical conversion is pretty fast: 0.3 ms

In [261]: b=scicore.array(a, dtype="S1")

In [262]: b
Out[262]: array([[[[[[[[[[[[[[[1]]]]]]]]]]]]]]], dtype=(string,1))

In [263]: t1=time(); c=numarray.strings.array(b);print time()-t1
0.61981511116      # string conversion is more than 1000x slower

In [264]: t1=time(); d=scicore.array(c);print time()-t1
0.000162839889526  # scipy_core speed seems normal

In [266]: t1=time(); d=numarray.strings.array(c);print time()-t1
1.38820910454      # converting numarray strings into themselves is
                   # the slowest!

Using numarray 1.5.0 and scipy_core 0.9.2.1763.

Cheers,



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