Say I have this array:
array = np.array([[1,2,3],[4,5,6],[7,8,9]])
Returns:
123
456
789
How should I go about getting it to return something like this?
111222333
111222333
111222333
444555666
444555666
444555666
777888999
777888999
777888999
You'd have to use np.repeat twice here.
np.repeat(np.repeat(array, 3, axis=1), 3, axis=0)
# [[1 1 1 2 2 2 3 3 3]
# [1 1 1 2 2 2 3 3 3]
# [1 1 1 2 2 2 3 3 3]
# [4 4 4 5 5 5 6 6 6]
# [4 4 4 5 5 5 6 6 6]
# [4 4 4 5 5 5 6 6 6]
# [7 7 7 8 8 8 9 9 9]
# [7 7 7 8 8 8 9 9 9]
# [7 7 7 8 8 8 9 9 9]]
For fun (because the nested repeat will be more efficient), you could use einsum on the input array and an array of ones that has extra dimensions to create a multidimensional array with the dimensions in an ideal order to reshape to the expected 2D shape:
np.einsum('ij,ikjl->ikjl', array, np.ones((3,3,3,3))).reshape(9,9)
The generic method being:
i,j = array.shape
k = 3 # extra rows
l = 3 # extra cols
np.einsum('ij,ikjl->ikjl', a, np.ones((i,k,j,l))).reshape(i*k,j*l)
Output:
array([[1, 1, 1, 2, 2, 2, 3, 3, 3],
[1, 1, 1, 2, 2, 2, 3, 3, 3],
[1, 1, 1, 2, 2, 2, 3, 3, 3],
[4, 4, 4, 5, 5, 5, 6, 6, 6],
[4, 4, 4, 5, 5, 5, 6, 6, 6],
[4, 4, 4, 5, 5, 5, 6, 6, 6],
[7, 7, 7, 8, 8, 8, 9, 9, 9],
[7, 7, 7, 8, 8, 8, 9, 9, 9],
[7, 7, 7, 8, 8, 8, 9, 9, 9]])
What is however nice with this method, is that it's quite easy to change the order to obtain other patterns or work with higher dimensions.
Example with other patterns:
>>> np.einsum('ij,iklj->iklj', a, np.ones((3,3,3,3))).reshape(9,9)
array([[1, 2, 3, 1, 2, 3, 1, 2, 3],
[1, 2, 3, 1, 2, 3, 1, 2, 3],
[1, 2, 3, 1, 2, 3, 1, 2, 3],
[4, 5, 6, 4, 5, 6, 4, 5, 6],
[4, 5, 6, 4, 5, 6, 4, 5, 6],
[4, 5, 6, 4, 5, 6, 4, 5, 6],
[7, 8, 9, 7, 8, 9, 7, 8, 9],
[7, 8, 9, 7, 8, 9, 7, 8, 9],
[7, 8, 9, 7, 8, 9, 7, 8, 9]])
>>> np.einsum('ij,kjil->kjil', a, np.ones((3,3,3,3))).reshape(9,9)
array([[1, 1, 1, 4, 4, 4, 7, 7, 7],
[2, 2, 2, 5, 5, 5, 8, 8, 8],
[3, 3, 3, 6, 6, 6, 9, 9, 9],
[1, 1, 1, 4, 4, 4, 7, 7, 7],
[2, 2, 2, 5, 5, 5, 8, 8, 8],
[3, 3, 3, 6, 6, 6, 9, 9, 9],
[1, 1, 1, 4, 4, 4, 7, 7, 7],
[2, 2, 2, 5, 5, 5, 8, 8, 8],
[3, 3, 3, 6, 6, 6, 9, 9, 9]])