Combination of conditions: Numpy array

Question

I'm trying to combine several numpy conditions, and its not adding as expected:

import numpy as np
ke, ku = np.arange(30, dtype=int), np.arange(50, dtype=int)
KE, KU = np.meshgrid(ke, ku, indexing='ij')

Now, the following works as expected:

>>> (KU > 0)[:5, :5] 
Out[28]: 
array([[False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True]], dtype=bool)

>>> (KE > 0)[:5, :5] 
Out[29]: 
array([[False, False, False, False, False],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True]], dtype=bool)

>>> ((KE > 0) & (KU > 0))[:5, :5] 
Out[31]: 
array([[False, False, False, False, False],
       [False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True],
       [False,  True,  True,  True,  True]], dtype=bool)

However in the next case, not so much:

>>> (KE + KU > 1)[:5, :5]
Out[24]: 
array([[False, False,  True,  True,  True],
       [False,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True]], dtype=bool)

>>> ((KE + KU > 1) & KE > 0)[:5, :5]
Out[19]: 
array([[False, False, False, False, False],
       [False,  True,  True,  True,  True],
       [False, False, False, False, False],
       [ True,  True,  True,  True,  True],
       [False, False, False, False, False]], dtype=bool)

I expected the following outcome - why didn't it happen?

array([[False, False, False, False, False],
       [False,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True],
       [ True,  True,  True,  True,  True]], dtype=bool)

Alessandro · Accepted Answer · 2016-03-23 17:49:13Z

4

This case looks correct to me: (KE + KU > 1)[:5, :5]

The second case is just a matter of parenthesis:

((KE + KU > 1) & (KE > 0))[:5, :5]

answered Mar 23, 2016 at 17:49

Alessandro

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