Perform a reverse cumulative sum on a numpy array

Question

Can anyone recommend a way to do a reverse cumulative sum on a numpy array?

Where \'reverse cumulative sum\' is defined as below (I welcome any corrections on the na

Answer 1

You can use .flipud() for this as well, which is equivalent to [::-1] https://docs.scipy.org/doc/numpy/reference/generated/numpy.flipud.html

In [0]: x = np.array([0,1,2,3,4])

In [1]: np.flipud(np.flipud(x).cumsum())
Out[1]: array([10, 10,  9,  7,  4]

.flip() is new as of NumPy 1.12, and combines the .flipud() and .fliplr() into one API. https://docs.scipy.org/doc/numpy/reference/generated/numpy.flip.html

This is equivalent, and has fewer function calls:

np.flip(np.flip(x, 0).cumsum(), 0)