Is there a MATLAB accumarray equivalent in numpy?

Question

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. An exampl

Answer 1

You can do this with pandas DataFrame in one line.

In [159]: df = pd.DataFrame({"y":np.arange(1,11),"x":[0,1,0,0,0,1,1,2,2,1]})

In [160]: df
Out[160]: 
   x   y
0  0   1
1  1   2
2  0   3
3  0   4
4  0   5
5  1   6
6  1   7
7  2   8
8  2   9
9  1  10

In [161]: pd.pivot_table(df,values='y',index='x',aggfunc=sum)
Out[161]: 
    y
x    
0  13
1  25
2  17

You can tell the pivot_table to use specific columns as indices and values, and get a new DataFrame object. When you specify the aggregation function as the sum the results will be identical to Matlab's accumarray.