[SciPy-User] MATLAB accumarray equivalent ?

[Alan G Isaac]

On 3/26/2010 10:39 AM, Mohammad Abdollahi wrote:
> Does anyone know what is the equivalent function of MATLAB's
> "accumarray()" in scipy/numpy,  with the exact same functionality ?

That certainly gets the basic accumarray functionality:

         >>> vals = 101+np.arange(5)
         >>> subs = np.array([1,2,4,2,4])-1
         >>> np.bincount(subs,vals)
         array([ 101.,  206.,    0.,  208.])

Here's another way that maybe easier
to adapt to whatever the OP needs:

         >>> from collections import defaultdict
         >>> d = defaultdict(float)
         >>> for i, cat in enumerate(subs):
         ...   d[cat] += vals[i]
         ...
         >>> d
         defaultdict(<type 'float'>, {0: 101.0, 1: 206.0, 3: 208.0})

That should actually be pretty fast,
though not as fast as bincount of course.

What's the use case?

hth,
Alan Isaac