A Dilluns 28 Març 2005 17:13, Francesc Altet va escriure: [snip]

Based on suggestions from Todd Miller on how to do this as efficiently as possible, I have arrived to the conclusions that the next conversions are the most efficient ones:

In [69]:na = numarray.arange(100*1000,shape=(100,1000)) In [70]:num = Numeric.arange(100*1000);num=num.resize((100,1000))

In [72]:t1=time();num2=Numeric.fromstring(na._data, typecode=na.typecode());num2=num2.resize(na.shape);time()-t1 Out[72]:0.0017759799957275391 In [73]:t1=time();na2=numarray.fromstring(num.tostring(),type=num.typecode(),s hape=num.shape);time()-t1 Out[73]:0.0039050579071044922

Er, sorry, there is in fact a more efficient way to convert from a Numeric object to a numarray object that doesn't require any data copy at all. This is: In [212]:num=Numeric.arange(100*1000, typecode="i");num=num.resize((100,1000)) In [213]:num[0,:5] Out[213]:array([0, 1, 2, 3, 4],'i') In [214]:t1=time();na2=numarray.array(numarray.memory.writeable_buffer(num),type=num.typecode(),shape=num.shape);time()-t1 Out[214]:0.0001010894775390625 # takes just 100 us! In [215]:na2[0,4] = 1 # modify a cell In [216]:num[0,:5] Out[216]:array([0, 1, 2, 3, 1],'i') In [217]:na2[0,:5] Out[217]:array([0, 1, 2, 3, 1]) # na2 has been modified as well, so the # data area is shared between num and na2 in fact, its speed is independent of the array size (as it should be for a non-data-copying procedure): # Create a Numeric object 10x larger In [218]:num=Numeric.arange(1000*1000, typecode="i");num=num.resize((1000,1000)) In [219]:t1=time();na2=numarray.array(numarray.memory.writeable_buffer(num),type=num.typecode(),shape=num.shape);time()-t1 Out[219]:0.00010204315185546875 # 100 us again! This is because numarray has chosen to use a buffer object internally, and that the Numeric object can be wrapped by a buffer object without any actual data copy. That drives me to think that, if the bytes object (that seems to be implemented by Numeric3) could wrap the buffer object where numarray objects hold its data, the conversion between Numeric3 <--> numarray (or, in general, between those packages that deal with bytes objects and other packages that deal with buffer objects) can be done with a cost of 1 (that is, independent of the data size). If this cannot be done (I mean, to get a safe bytes object from a buffer object and vice-versa), well, it should be a pity. Do you think that would be possible at all? Cheers, --

qo< Francesc Altet http://www.carabos.com/ V V Cárabos Coop. V. Enjoy Data ""