Indexing: Selecting columns with booleans

[Yannick Jadoul]

Something goes wrong, indexing a 2D array with an array of booleans to select columns. Instead of selecting the columns, the rows are selected and reshaped.

Simple minimal example, hopefully clarifying what I mean:

>>>> x = np.array([[i + 2*j for j in range(10)]for i in range(10)])
>>>> b = np.array([True,False] * 5)
>>>> x
array([[ 0,  2,  4,  6,  8, 10, 12, 14, 16, 18],
       [ 1,  3,  5,  7,  9, 11, 13, 15, 17, 19],
       [ 2,  4,  6,  8, 10, 12, 14, 16, 18, 20],
       [ 3,  5,  7,  9, 11, 13, 15, 17, 19, 21],
       [ 4,  6,  8, 10, 12, 14, 16, 18, 20, 22],
       [ 5,  7,  9, 11, 13, 15, 17, 19, 21, 23],
       [ 6,  8, 10, 12, 14, 16, 18, 20, 22, 24],
       [ 7,  9, 11, 13, 15, 17, 19, 21, 23, 25],
       [ 8, 10, 12, 14, 16, 18, 20, 22, 24, 26],
       [ 9, 11, 13, 15, 17, 19, 21, 23, 25, 27]])
>>>> b
array([ True, False,  True, False,  True, False,  True, False,  True, False], dtype=bool)
>>>> x[b,:]
array([[ 0,  2,  4,  6,  8, 10, 12, 14, 16, 18],
       [ 2,  4,  6,  8, 10, 12, 14, 16, 18, 20],
       [ 4,  6,  8, 10, 12, 14, 16, 18, 20, 22],
       [ 6,  8, 10, 12, 14, 16, 18, 20, 22, 24],
       [ 8, 10, 12, 14, 16, 18, 20, 22, 24, 26]])
>>>> x[:,b]
array([[ 0,  2,  4,  6,  8],
       [10, 12, 14, 16, 18],
       [ 2,  4,  6,  8, 10],
       [12, 14, 16, 18, 20],
       [ 4,  6,  8, 10, 12],
       [14, 16, 18, 20, 22],
       [ 6,  8, 10, 12, 14],
       [16, 18, 20, 22, 24],
       [ 8, 10, 12, 14, 16],
       [18, 20, 22, 24, 26]])

EDIT

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[PyPy 5.4.1 with GCC 4.8.2] on linux2
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