Numpy vectorized and unvectorized code results not matching for 3d array

Question

I am trying to refactor procedural code of a numpy 3d array into it's vectorized equivalent and the results are not matching .

import numpy as np 
              
arr = np.empty((16,73,144))

boolArray = np.zeros((14,73,144)) 

for k in range(0,16): 
   for j in range(0,73): 
      for i in range(0,144): 
        if (k == 0):
            doSomething():
        else if (k == 15):
             doSomething():
        else:
         if (arr[k+1,j,i] == arr[k-1,j,i]): 
              boolArray[k,j,i] = True

The vectorized counterpart -

# isArrEqual is a boolean array of identical shape to boolArray 
isArrEqual = (arr[2:,:,:] == arr[0:-2,:,:])

In my real data I get 6000 true entries for the procedural code and no trues at all in the vectorized counterpart.

Where I am going wrong ?

arr = np.empty(16,73,144) should be arr = np.empty((16,73,144)). Same for boolArray — Corralien
– Corralien, Commented Oct 21, 2021 at 7:01

Alexander Volkovsky · Accepted Answer · 2021-10-21 07:08:56Z

1

You probably have a mistake in your procedural code. I believe it should be

for k in range(1, 15):  # changed 14 to 15 
   for j in range(0,73): 
      for i in range(0,144): 
         if (arr[k+1,j,i] == arr[k-1,j,i]): 
              boolArray[k-1,j,i] = True  # changed k to k-1

I don't see any issues in the numpy code.

answered Oct 21, 2021 at 7:08

Alexander Volkovsky

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6 Comments

gansub Over a year ago

Am I allowed to make an edit to the question based on your answer?

Alexander Volkovsky Over a year ago

But doesn't that solve your problem?

gansub Over a year ago

No it does not. So can I make an edit ?

Alexander Volkovsky Over a year ago

Yes. please be precise with data types in arrays

Alexander Volkovsky Over a year ago

@gansub, you still have issues in your procedural code. (IndexError for k = 14 + syntax errors, + you didn't changed k to k - 1 in the last line)

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