Suppose I have the following 4 by 3 by 3 array,
array([[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]],
[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]],
[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]],
[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]]])
I would like to filter such array by the following standards: Treat each 3 by 3 array as a block, if all elements in this block = -2, we should cut the whole block, so the target array would look like this(1 by 3 by 3):
array([[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]]])
I could only come up with brutal solution with if loop, but it does not meet the requirements, so anybody can share a better method?
You can recreate the original array by the following commands
array = np.array([[-2,-2,-2,-2,-2,-2,-2,-2,-2],
[-2,-2,-2,-2,-2,-2,-2,-2,-2],
[-2,-2,71,-1,-1,-1,71,-1,52],
[-2,-2,-2,-2,-2,-2,-2,-2,-2]])
newarr = array.reshape(4,3,3)
CodePudding user response:
The other answers are nice if you expect your arrays along axis 0 to always be a specific value, like -2, or 872385, etc.
In case you want something more general where you want to filter out any arrays which contain a single value, you can filter arrays by rank.
Since any matrix of a single value will have rank 1, you can filter by rank != 1
:
In [2]: x[np.linalg.matrix_rank(x) != 1]
Out[2]:
array([[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]]])
This will work for any matrix along axis 0 which is filled with the same values. Another example:
In [4]: x
Out[4]:
array([[[ 5, 5, 5],
[ 5, 5, 5],
[ 5, 5, 5]],
[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]],
[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]],
[[99, 99, 99],
[99, 99, 99],
[99, 99, 99]]])
In [5]: x[np.linalg.matrix_rank(x) != 1]
Out[5]:
array([[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]]])
CodePudding user response:
You can do this, it uses the filter array feature and the all()
function in NumPy :
filterarr = []
for arr in newarr:
if np.all(arr==-2):
filterarr.append(False)
else:
filterarr.append(True)
newarr = newarr[filterarr]
print(newarr)
CodePudding user response:
You can use np.where
:
data[np.where(np.any(data != -2, axis=-1))]
With the given array as data
, the output is:
[[-2 -2 71]
[-1 -1 -1]
[71 -1 52]]
CodePudding user response:
You can just select for the negation of where all the array along the 2nd and 3rd axes are equal to -2
:
>>> arr
array([[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]],
[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]],
[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]],
[[-2, -2, -2],
[-2, -2, -2],
[-2, -2, -2]]])
>>> ~(arr == -2).all(axis=(1,2))
array([False, False, True, False])
And use boolean indexing on the first axis:
>>> arr[~(arr == -2).all(axis=(1,2)), ...]
array([[[-2, -2, 71],
[-1, -1, -1],
[71, -1, 52]]])