How can I get the row and column number of a numpy 2d array meeting a specified condition? For example, I have a 2d array (all float numbers) and I want to get the location (row and column index) where the minimum or maximum values is.
You can use np.where()
as in the following example:
In [46]: arr = np.arange(10, dtype=float32).reshape(5, 2)
In [47]: arr
Out[47]:
array([[ 0., 1.],
[ 2., 3.],
[ 4., 5.],
[ 6., 7.],
[ 8., 9.]], dtype=float32)
# get row and column index of minimum value in arr
In [48]: np.where(arr == arr.min())
Out[48]: (array([0]), array([0]))
# get the indices of maximum element in arr
In [49]: np.where(arr == arr.max())
Out[49]: (array([4]), array([1]))
The above approach also works even if you have multiple minimum/maximum values in your array.
In [59]: arr
Out[59]:
array([[ 0., 0.],
[ 2., 3.],
[ 4., 5.],
[ 6., 7.],
[ 9., 9.]], dtype=float32)
In [60]: np.where(arr == arr.max())
Out[60]: (array([4, 4]), array([0, 1])) # positions: (4,0) and (4,1)
In [61]: np.where(arr == arr.min())
Out[61]: (array([0, 0]), array([0, 1])) # positions: (0,0) and (0,1)
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