[Numpy-discussion] Multidimensional Indexing
Nicholas Devenish
misnomer at gmail.com
Mon Apr 6 19:49:34 EDT 2015
With the indexing example from the documentation:
y = np.arange(35).reshape(5,7)
Why does selecting an item from explicitly every row work as I’d expect:
>>> y[np.array([0,1,2,3,4]),np.array([0,0,0,0,0])]
array([ 0, 7, 14, 21, 28])
But doing so from a full slice (which, I would naively expect to mean “Every Row”) has some…other… behaviour:
>>> y[:,np.array([0,0,0,0,0])]
array([[ 0, 0, 0, 0, 0],
[ 7, 7, 7, 7, 7],
[14, 14, 14, 14, 14],
[21, 21, 21, 21, 21],
[28, 28, 28, 28, 28]])
What is going on in this example, and how do I get what I expect? By explicitly passing in an extra array with value===index? What is the rationale for this difference in behaviour?
Thanks,
Nick
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