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numpynumpy-ndarraynumpy-slicing

Reversing order of second column only in for a 2x2 ND-Array

Right now I have a 2x2 ND-array, namely np.array([[93, 95], [84, 100], [99, 87]]). I would like to reverse the second column of the array into, such that I get: np.array([[93, 87], [84, 100], [99, 95]]).

I tried the following code:

grades = np.array([[93,  95], [84, 100], [99,  87]])
print(grades[::-1,:])

However, the result I get is

[[ 99  87]
 [ 84 100]
 [ 93  95]]

I understand that this is because I am reversing all of the entries in the 1-axis, which is why the entries in the first column is also reversed. So what code can I write to get:

[[ 93  87]
 [ 84 100]
 [ 99  95]]
Solution

  • Use numpy.flip function to reverse the order of values in specific column(s), though it's more suitable for a more extended/general cases:

    grades = np.array([[93,  95], [84, 100], [99,  87], [99, 83]])
grades[:, -1] = np.flip(grades[:, -1])
print(grades)

    Or just use the reversed order of rows:

    grades[:, -1] = grades[::-1, -1]

    [[ 93  83]
 [ 84  87]
 [ 99 100]
 [ 99  95]]