CODEWITHSUNDEEP
pythonpandasdataframemultiplication
Korean_Of_the_Mountain
Korean_Of_the_Mountain

Reputation: 1577

Multiplying specific columns of dataframe by constant scalar value

How do I multiply only specific columns of a dataframe by a constant value?

df0 = pd.DataFrame({'A' : 1.,
                    'B' : 1,
                    'C' : 1,
                    'D' : np.array([1] * 4,dtype='int32')})

mult_by_two = df0.iloc[:,2:].mul(2)
print mult_by_two

I get this:

   C  D
0  2  2
1  2  2
2  2  2
3  2  2

but what I want is this:

   A  B  C  D
0  1  1  2  2
1  1  1  2  2
2  1  1  2  2
3  1  1  2  2

Upvotes: 2

Views: 14122

Answers (2)

Anton Protopopov
Anton Protopopov

Reputation: 31672

If you need to multiply on scalar you don't need to call mul method you could use usual * operator:

In [24]: df0.iloc[:,2:] * 2
Out[24]: 
   C  D
0  2  2
1  2  2
2  2  2
3  2  2

For your question you could use pd.concat with your first columns and columns you are multiplying:

In [25]: pd.concat([df0.iloc[:,:2], df0.iloc[:,2:] * 2], axis=1)
Out[25]: 
   A  B  C  D
0  1  1  2  2
1  1  1  2  2
2  1  1  2  2
3  1  1  2  2

Upvotes: 2

Mike Müller
Mike Müller

Reputation: 85482

You can assign the result to df0:

>>> df0.iloc[:,2:] = df0.iloc[:,2:].mul(2)
>>> df0

   A  B  C  D
0  1  1  2  2
1  1  1  2  2
2  1  1  2  2
3  1  1  2  2

If you want a copy, make before the assigment:

df1 = df0.copy()
df1.iloc[:,2:] = df1.iloc[:,2:].mul(2)

Upvotes: 6

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