Python: sum over arrays element by element

Question

I have some probability output of 5 models, and I sum of the probabilities element by element like below:

probs = [None] * 5

for i in range(0,5):
  probs[i] = models[i].predict_proba(X)

probs[0] + probs[1] + probs[2] + probs[3] + probs[4]

This works fine.

I then tried to simplified the above code a bit by doing below:

probs = [None] * 5
results = [None]

for i in range(0,5):
  probs[i] = models[i].predict_proba(X)
  results += probs[i]

results

But got the following error:

TypeError unsupported operand type(s) for +: 'NoneType' and 'float' 
TypeErrorTraceback (most recent call last)
<ipython-input-20-8d4d443a7428> in <module>()
      4 for i in range(0,5):
      5   probs[i] = models[i].predict_proba(X)
----> 6   results += probs[i]
      7 
      8 results

TypeError: unsupported operand type(s) for +: 'NoneType' and 'float'

How could I fix such error? Thanks.

Note: 

probs[i] is of format:

array([[  9.99877759e-01,   1.22241455e-04],
       [  9.99694005e-01,   3.05994629e-04],
       [  9.47546608e-01,   5.24533925e-02],
       [  1.83994998e-01,   8.16005002e-01],
       [  9.66928729e-01,   3.30712706e-02],
       [  9.99487283e-01,   5.12717255e-04],
       [  2.85824823e-03,   9.97141752e-01],
       [  9.97979081e-01,   2.02091861e-03],
       [  9.99744813e-01,   2.55186665e-04]])

Just set results = 0 and your code will run fine. However, you should really consider the answers below as they are more pythonic. — Autonomous
– Autonomous, Commented Mar 30, 2018 at 23:08

user3483203 · Accepted Answer · 2018-03-30 23:01:25Z

3

Your issue is that you are trying to add a float to None. You can simplify your code greatly using a list comprehension:

probs = [models[i].predict_proba(X) for i in range(5)]

And then to get the sum, just sum(probs)

answered Mar 30, 2018 at 23:01

user3483203

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JACK ZHANG · Accepted Answer · 2018-03-30 23:04:23Z

2

You assigned [None] as your result at the beginning, and then try to add it immediately in the first iteration of the for loop, and that causes the error message.

Instead, you can try use list comprehension since using Python:

result = sum([models[i].predict_proba(X) for i in range(5)])

answered Mar 30, 2018 at 23:04

JACK ZHANG

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StackOverPine · Accepted Answer · 2018-03-30 23:18:20Z

1

You defined result as a list, but it should be a float type. Try this:

results = 0

answered Mar 30, 2018 at 23:18

StackOverPine

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Bill · Accepted Answer · 2018-03-30 23:24:39Z

0

This should solve the problem:

probs = [None] * 5
results = np.zeros(data.shape)

for i in range(0,5):
  probs[i] = models[i].predict_proba(X)
  results += probs[i]

results

Where, data.shape should be the expected shape of the result from models[i].predict_proba(X).

answered Mar 30, 2018 at 23:24

Bill

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