[Numpy-discussion] custom accumlators

[Karol Langner]

On Friday 05 of January 2007 17:42, Matt Knox wrote:
> ---------------------------------------------
> Example 1 - exponential moving average:
>
> # naive brute force method...
> def expmave(x, k):
>     result = numpy.array(x, copy=True)
>     for i in range(1, result.size):
>        result[i] = result[i-1] + k * (result[i] - result[i-1])
>     return result
>
> # slicker method (if it worked, which it doesn't)...
> def expmave(x, k):
>     def expmave_sub(a, b):
>         return a + k * (b - a)
>     return numpy.vectorize(expmave_sub).accumulate(x)

Why can't you simply use list comprehensions? Too slow?

For example:
def expmave(x, k):
	return [x[0]] + [x[i-1] + k*(x[i]-x[i-1]) for i in range(1,len(x))]

Karol

-- 
written by Karol Langner
Fri Jan  5 17:58:27 CET 2007