[Numpy-discussion] Efficiently converting a numarray object to Numeric

Todd Miller jmiller at stsci.edu
Wed Feb 9 08:38:13 CST 2005


On Wed, 2005-02-09 at 11:27 -0500, Todd Miller wrote:
> On Wed, 2005-02-09 at 16:37 +0100, Francesc Altet wrote:
> > Hi,
> > 
> > I'm wondering if there is a more efficient way to convert a numarray
> > object into a Numeric one than:
> > 
> > >>> import Numeric
> > >>> import numarray
> > >>> from time import time
> > >>> a = numarray.arange(100*1000)
> > >>> t1=time();b=Numeric.array(a);time()-t1
> > 0.43448090553283691
> > 
> > Any suggestions?
> 
> Yes!  
> 
> import Numeric
> import numarray
> from time import time
> 
> a = numarray.arange(100*1000)
> 
> t1=time();b=Numeric.array(a);
> print time()-t1
> 
> t1 = time();  c=Numeric.fromstring(a._data, typecode='i')
> print time()-t1
> 
> print b[-10:]
> print c[-10:]
>       
> I get:
> 
> 1.58109998703
> 0.00659704208374
> [99990 99991 99992 99993 99994 99995 99996 99997 99998 99999]
> [99990 99991 99992 99993 99994 99995 99996 99997 99998 99999]
> 
> Note that in CVS,  fromstring(a, typecode='i') now also works because
> numarray now supplies the buffer protocol as well as consuming buffers.
> 

One more thing is necessary to handle a misbehaved numarray and make its
buffer usable by Numeric:

if not a.is_c_array():
	a = a.copy()

Regards,
Todd







More information about the Numpy-discussion mailing list