Re: Numeric/Numarray equivalent to zip ?
"Peter Otten" <[EMAIL PROTECTED]> wrote: > George Sakkis wrote: > > > Though not the fastest to execute; using concatenate instead of > > initializing an array from a list [a,a] is more than 2,5 time faster in > > my system (~4.6 vs 11.8 usec per loop according to timeit.py), and it's > > not harder either. > > That surprises me. I would expect essentially the same amount of > data-shuffling. Here are some timing comparisons of four versions I tried. The first three work on 1D arrays directly and the fourth on 2D row arrays (i.e. shape (1,len(a))): from Numeric import * # 11.5 usec/loop def ziparrays_1(*arrays): return array(arrays) # 8.1 usec/loop def ziparrays_2(*arrays): a = zeros((len(arrays),len(arrays[0]))) for i in xrange(len(arrays)): a[i] = arrays[i] return a # 13.6 usec/loop def ziparrays_3(*arrays): return reshape(concatenate(arrays), (len(arrays),len(arrays[0]))) # 4.6 usec/loop def ziparrays_4(*arrays): return concatenate(arrays) So if one has the choice, it's better to start with 2D arrays instead of 1D. Comparing versions 3 and 4, it's surprising that reshape takes twice as much as concatenate. George -- http://mail.python.org/mailman/listinfo/python-list
Re: Numeric/Numarray equivalent to zip ?
George Sakkis wrote: > Though not the fastest to execute; using concatenate instead of > initializing an array from a list [a,a] is more than 2,5 time faster in > my system (~4.6 vs 11.8 usec per loop according to timeit.py), and it's > not harder either. That surprises me. I would expect essentially the same amount of data-shuffling. > One difference is that the equivalent expression for > concatenate expects arrays of shape (1,len(a)) instead of 1D arrays os > shape (len(a),): If you want to start out with 1D arrays, just reorder the operations: >>> a = array(range(5)) >>> reshape(concatenate((a, a)), (2, 5)) array([[0, 1, 2, 3, 4], [0, 1, 2, 3, 4]]) >>> Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Numeric/Numarray equivalent to zip ?
"Peter Otten" <[EMAIL PROTECTED]> wrote: > George Sakkis wrote: > > > What's the fastest and most elegant equivalent of zip() in > > Numeric/Numarray between two equally sized 1D arrays ? That is, how to > > combine two (N,)-shaped arrays to one (N,2) (or (2,N)) shaped ? I > > expect the fastest and the most elegant idiom to be identical, as it is > > usually the case in this excellent library, but if not, both would be > > useful to know. Thanks, > > >>> import Numeric as nu > >>> a = nu.array(range(3)) > >>> nu.array([a, a]) > array([[0, 1, 2], >[0, 1, 2]]) > >>> nu.transpose(nu.array([a, a])) > array([[0, 0], >[1, 1], >[2, 2]]) > > Or am I missing something? As to speed, it seems to be the fastest to > write... Though not the fastest to execute; using concatenate instead of initializing an array from a list [a,a] is more than 2,5 time faster in my system (~4.6 vs 11.8 usec per loop according to timeit.py), and it's not harder either. One difference is that the equivalent expression for concatenate expects arrays of shape (1,len(a)) instead of 1D arrays os shape (len(a),): >>> a = reshape(range(5), (1,5)) >>> a array([ [0, 1, 2, 3, 4]]) >>> concatenate((a,a)) array([[0, 1, 2, 3, 4], [0, 1, 2, 3, 4]]) George -- http://mail.python.org/mailman/listinfo/python-list
Re: Numeric/Numarray equivalent to zip ?
George Sakkis wrote: > What's the fastest and most elegant equivalent of zip() in > Numeric/Numarray between two equally sized 1D arrays ? That is, how to > combine two (N,)-shaped arrays to one (N,2) (or (2,N)) shaped ? I > expect the fastest and the most elegant idiom to be identical, as it is > usually the case in this excellent library, but if not, both would be > useful to know. Thanks, >>> import Numeric as nu >>> a = nu.array(range(3)) >>> nu.array([a, a]) array([[0, 1, 2], [0, 1, 2]]) >>> nu.transpose(nu.array([a, a])) array([[0, 0], [1, 1], [2, 2]]) Or am I missing something? As to speed, it seems to be the fastest to write... Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Numeric/Numarray equivalent to zip ?
George Sakkis wrote: What's the fastest and most elegant equivalent of zip() in Numeric/Numarray between two equally sized 1D arrays ? That is, how to combine two (N,)-shaped arrays to one (N,2) (or (2,N)) shaped ? I expect the fastest and the most elegant idiom to be identical, as it is usually the case in this excellent library, but if not, both would be useful to know. Thanks, Look at combining concatenate(), reshape(), and transpose(). In Scipy, I would use hstack() and vstack(). -- Robert Kern [EMAIL PROTECTED] "In the fields of hell where the grass grows high Are the graves of dreams allowed to die." -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list
Numeric/Numarray equivalent to zip ?
What's the fastest and most elegant equivalent of zip() in Numeric/Numarray between two equally sized 1D arrays ? That is, how to combine two (N,)-shaped arrays to one (N,2) (or (2,N)) shaped ? I expect the fastest and the most elegant idiom to be identical, as it is usually the case in this excellent library, but if not, both would be useful to know. Thanks, George -- http://mail.python.org/mailman/listinfo/python-list
