Do you know about N.fromiter() ? -Sebastian Haase
On Dec 14, 2007 12:33 AM, Jonathan Taylor <[EMAIL PROTECTED]> wrote: > I was needing an array representation of ndindex since ndindex only > gives an iterator but array(list(ndindex)) takes too long. There is > prob some obvious way to do this I am missing but if not feel free to > include this code which is much faster. > > In [252]: time a=np.array(list(np.ndindex(10,10,10,10,10,10))) > CPU times: user 11.61 s, sys: 0.09 s, total: 11.70 s > Wall time: 11.82 > > In [253]: time a=ndtuples(10,10,10,10,10,10) > CPU times: user 0.32 s, sys: 0.21 s, total: 0.53 s > Wall time: 0.60 > > def ndtuples(*dims): > """Fast implementation of array(list(ndindex(*dims))).""" > > # Need a list because we will go through it in reverse popping > # off the size of the last dimension. > dims = list(dims) > > # N will keep track of the current length of the indices. > N = dims.pop() > > # At the beginning the current list of indices just ranges over the > # last dimension. > cur = np.arange(N) > cur = cur[:,np.newaxis] > > while dims != []: > > d = dims.pop() > > # This repeats the current set of indices d times. > # e.g. [0,1,2] -> [0,1,2,0,1,2,...,0,1,2] > cur = np.kron(np.ones((d,1)),cur) > > # This ranges over the new dimension and 'stretches' it by N. > # e.g. [0,1,2] -> [0,0,...,0,1,1,...,1,2,2,...,2] > front = np.arange(d).repeat(N)[:,np.newaxis] > > # This puts these two together. > cur = np.column_stack((front,cur)) > N *= d > > return cur > _______________________________________________ > Numpy-discussion mailing list > [email protected] > http://projects.scipy.org/mailman/listinfo/numpy-discussion > _______________________________________________ Numpy-discussion mailing list [email protected] http://projects.scipy.org/mailman/listinfo/numpy-discussion
