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DS-1000 / 407 / I'm looking for a fast solution to MATLAB's accumarray in numpy. The accumarray…

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Problem:
I'm looking for a fast solution to MATLAB's accumarray in numpy. The accumarray accumulates the elements of an array which belong to the same index.
Note that there might be negative indices in accmap, and we treat them like list indices in Python.
 An example:
a = np.arange(1,11)
# array([ 1,  2,  3,  4,  5,  6,  7,  8,  9, 10])
accmap = np.array([0,1,0,0,0,-1,-1,2,2,1])
Result should be
array([13, 12, 30])
Is there a built-in numpy function that can do accumulation like this? Using for-loop is not what I want. Or any other recommendations?
A:
<code>
import numpy as np
a = np.arange(1,11)
accmap = np.array([0,1,0,0,0,-1,-1,2,2,1])
</code>
result = ... # put solution in this variable
BEGIN SOLUTION
<code>

library

Numpy

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Source and history

upstream_id / Original problem ID
407
task_id
332abdd1-b7e7-5e8d-a09f-0d79673302f9
task_key
default--test--407
task_revision_id
1
config / split
default / test

Official source

initial import