What meaning is '[: , None]'?
Steven D'Aprano
steve at pearwood.info
Sat Jan 2 10:39:36 EST 2016
On Sat, 2 Jan 2016 11:44 pm, Robert wrote:
> Hi,
>
> I read a code snippet, in which object w_A is:
>
>
> w_A
> Out[48]: array([ 0.10708809, 0.94933575, 0.8412686 , 0.03280939,
> 0.59985308])
w_A looks like a numpy array of five values.
http://docs.scipy.org/doc/numpy/reference/arrays.html
> Then, I don't know what is '[: ' below:
> vs_A = w_A[:, None] * xs
The syntax w_A[ ... ] is a "slice" of array w_A. Slicing means to create a
new array from part of the original.
None inside a numpy slice behaves as an alias for numpy.newaxis.
http://docs.scipy.org/doc/numpy/reference/arrays.indexing.html
In this case, w_A[:, None] returns a "view" of the original w_A array.
--
Steven
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