How can I simultaneously select all odd rows and all even columns of an array

Question

I\'m new to programming and I need a program, that can select all odd rows and all even columns of a Numpy array at the same time in one code. here is what I tried:

Answer 1

Let's say you have this array, x:

>>> import numpy
>>> x = numpy.array([[ 1,  2,  3,  4,  5],
... [ 6,  7,  8,  9, 10],
... [11, 12, 13, 14, 15],
... [16, 17, 18, 19, 20]])

To get every other odd row, like you mentioned above:

>>> x[::2]
array([[ 1,  2,  3,  4,  5],
       [11, 12, 13, 14, 15]])

To get every other even column, like you mentioned above:

>>> x[:, 1::2]
array([[ 2,  4],
       [ 7,  9],
       [12, 14],
       [17, 19]])

Then, combining them together yields:

>>> x[::2, 1::2]
array([[ 2,  4],
       [12, 14]])

For more details, see the Indexing docs page.

Answer 2

Slicing an array:

import numpy as np

arr = np.array([[1, 2, 3], [4, 5, 6],[7, 8, 9],[10, 11, 12],[13, 14, 15]])

case1=arr[::2,:]    #odd rows
case2=arr[1::2,:]   #even rows
case3=arr[:,::2]    #odd cols
case4=arr[:,1::2]   #even cols
print(case1)
print("\n") 
print(case2)
print("\n") 
print(case3)
print("\n") 
print(case4)
print("\n")      

Gives:

[[ 1  2  3]
 [ 7  8  9]
 [13 14 15]]


[[ 4  5  6]
 [10 11 12]]


[[ 1  3]
 [ 4  6]
 [ 7  9]
 [10 12]
 [13 15]]


[[ 2]
 [ 5]
 [ 8]
 [11]
 [14]]

Answer 3

To get every other odd column:

 x[:,0::2]