Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

generalized cumulative functions in NumPy/SciPy?

Is there a function in numpy or scipy (or some other library) that generalizes the idea of cumsum and cumprod to arbitrary function. For example, consider the (theoretical) function

cumf( func, array) 

func is a function that accepts two floats, and returns a float. Particular cases

lambda x,y: x+y 

and

lambda x,y: x*y 

are cumsum and cumprod respectively. For example, if

func = lambda x,prev_x: x^2*prev_x 

and I apply it to:

cumf(func, np.array( 1, 2, 3) )

I would like

np.array( 1, 4, 9*4 )
like image 384
Cam.Davidson.Pilon Avatar asked Dec 11 '12 21:12

Cam.Davidson.Pilon


1 Answers

The ValueError above is still a bug using Numpy 1.20.1 (with Python 3.9.1).

Luckily a workaround was discovered that uses casting: https://groups.google.com/forum/#!topic/numpy/JgUltPe2hqw

import numpy as np
uadd = np.frompyfunc(lambda x, y: x + y, 2, 1)
uadd.accumulate([1,2,3], dtype=object).astype(int)
# array([1, 3, 6])

Note that since the custom operation works on an object type, it won't benefit from the efficient memory management of numpy. So the operation may be slower than one that didn't need casting to object for extremely large arrays.

like image 68
user2561747 Avatar answered Oct 18 '22 20:10

user2561747