On Tue, Jan 21, 2014 at 8:34 AM, Dr. Leo email@example.com wrote:
I would like to write something like:
In : iterable=((i, i**2) for i in range(10))
In : a=np.fromiter(iterable, int32)
ValueError Traceback (most recent call last) <ipython-input-26-5bcc2e94dbca> in <module>() ----> 1 a=np.fromiter(iterable, int32)
ValueError: setting an array element with a sequence.
Is there an efficient way to do this?
Perhaps you could just utilize structured arrays ( http://docs.scipy.org/doc/numpy/user/basics.rec.html), like: iterable= ((i, i**2) for i in range(10)) a= np.fromiter(iterable, [('a', int32), ('b', int32)], 10) a.view(int32).reshape(-1, 2) Out: array([[ 0, 0], [ 1, 1], [ 2, 4], [ 3, 9], [ 4, 16], [ 5, 25], [ 6, 36], [ 7, 49], [ 8, 64], [ 9, 81]])
My 2 cents, -eat
Creating two 1-dimensional arrays first is costly as one has to iterate twice over the data. So the only way I see is creating an empty [10,2] array and filling it row by row. This is memory-efficient but slow. List comprehension is vice versa.
If there is no solution, wouldn't it be possible to rewrite fromiter so as to accept sequences?
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