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I have a numpy array like

x=np.array([1,2,3,4])

I want to create another numpy array y which is the cumulative sum of x, so that

y=np.array([1,3,6,10])

What is a good num-Pythonic way to do this?

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2 Answers 2

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27 
y = np.cumsum(x)

See http://docs.scipy.org/doc/numpy/reference/generated/numpy.cumsum.html

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1 Comment

@Dan , Can I get the result in-place. I want the result is also in x, not another array y
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Another option is:

y = np.add.accumulate(x)

which is often times faster than np.cumsum even though the documentation says they are equivalent.

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I would like to say that I also tested this and accumulate is slightly faster on my system too: %timeit np.add.accumulate(range(20000000)) ---> 3.06 s ± 40.1 and for cumsum I get 3.08 s ± 24.7 ms

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