I have two 2d numpy arrays X and Y that look like:
X = np.array([[1,2,3,4],[4,5,6,7],[4,3,2,1],[7,8,9,0]]
)
Y = np.array([[0,0,0],[1,2,4],[1,1,1], [0,0,0]]
)
I want to remove all the arrays in Y that are all 0's (ie np.zeros), and all the corresponding arrays at the same index in the X array.
So, for these two X,Y arrays, I'd like back:
X = np.array([[4,5,6,7],[4,3,2,1]]
)
Y = np.array([[1,2,4],[1,1,1]]
)
X and Y will always have the same length, and X and Y will always be rectangular (ie every array within X will have the same length, and every array within Y will have the same length).
I tried using a loop but that doesn't seem to be as effective for large X and Y
Create a boolean array indicating any non zero element for each row and then filter with boolean array indexing :
any_zero = (Y != 0).any(1)
X[any_zero]
#[[4 5 6 7]
# [4 3 2 1]]
Y[any_zero]
#[[1 2 4]
# [1 1 1]]
First you will need to get a mask of which rows of Y are all zeros. This can be done with the any method and setting the axis to 1
Y.any(axis = 1)
Will return array([False, True, True, False])
You can use this array to get which rows you want to return from X and Y
X[Y.any(axis = 1)]
will return
array([[4, 5, 6, 7],
[4, 3, 2, 1]])
and
Y[Y.any(axis = 1)]
will return
array([[1, 2, 4],
[1, 1, 1]])
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