nitin nitin - 5 days ago 6
Python Question

Matrix Multiplication of a Pandas DataFrame and Series

I want to do a matrix multiplcation of a pandas dataframe and a series

df = pandas.DataFrame({'a':[4,1,3], 'b':[5,2,4]},index=[1,2,3])
ser = pandas.Series([0.6,0.4])


df is,

a b
1 4 5
2 1 2
3 3 4


ser is,

0 0.6
1 0.4


My desired result is a matrix product, like so

ans is,

I can do this by using numpy dot operator and rebuilding my dataFrame

c = a.values.dot(b.transpose())
c = pandas.DataFrame(c, index = a.index, columns = ['ans'])
print c


ans
1 4.4
2 1.4
3 3.4


Is there a native method in pandas to do this?

Answer

pandas implicity aligns on the index of a series, use the dot function

In [3]: df = pd.DataFrame({'a' : [4,1,3], 'b' : [5,2,4]},index=[1,2,3])

In [4]: s = pd.Series([0.6,0.4],index=['a','b'])

In [5]: df.dot(s)
Out[5]: 
1    4.4
2    1.4
3    3.4
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