Trying to get the maximum value every 12th element-CodePudding

I am trying to get the maximum of the first axis (of a 3d array), but get the maximum for only every 12th element.

Using a random 3D numpy array (that has the first axis divisible by 12), the first axis is a size of 36. and I want to get the maximum of the first 12 elements, then 12 - 24, and then 24 - 36.

I tried:

## 3d array

array = np.random.rand(36,20,30)

# get the maximum for every 12 units:

maximum_every_12 = np.zeros((int(array.shape[0]/12),array.shape[1],array.shape[2]))

for i in range(12):
    maximum_every_12[i,:,:] = np.max(array[i::12,:,:],axis=0)

but I get an index error:

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
/tmp/ipykernel_1643197/1714711606.py in <module>
      8 
      9 for i in range(12):
---> 10     maximum_every_12[i,:,:] = np.max(array[i::12,:,:],axis=0)

IndexError: index 3 is out of bounds for axis 0 with size 3

How might I get the maximum value for every 12th element based on the first axis of the 3d array (size 36, 20, 30).

CodePudding user response：

You have the size of the arrays wrong. The first axis of maximum_every_12 is of length 36 / 12 which is 3. Therefore you cannot iterate over range(12), which fails at i = 4. You must iterate over range(36/12).