How to subtract one data frame from another?

Let me first create a scene.

I am starting with a pandas

dataframe klmn

that looks like this:

In [15]: klmn
Out[15]: 
    K  L         M   N
0   0  a -1.374201  35
1   0  b  1.415697  29
2   0  a  0.233841  18
3   0  b  1.550599  30
4   0  a -0.178370  63
5   0  b -1.235956  42
6   0  a  0.088046   2
7   0  b  0.074238  84
8   1  a  0.469924  44
9   1  b  1.231064  68
10  2  a -0.979462  73
11  2  b  0.322454  97

      

        
        
        
      

    

Then I split klmn

into two data frames klmn0

and klmn1

according to the value in the "K" column:

In [16]: k0 = klmn.groupby(klmn['K'] == 0)
In [17]: klmn0, klmn1 = [klmn.ix[k0.indices[tf]] for tf in (True, False)]
In [18]: klmn0, klmn1
Out[18]: 
(   K  L         M   N
0  0  a -1.374201  35
1  0  b  1.415697  29
2  0  a  0.233841  18
3  0  b  1.550599  30
4  0  a -0.178370  63
5  0  b -1.235956  42
6  0  a  0.088046   2
7  0  b  0.074238  84,
     K  L         M   N
8   1  a  0.469924  44
9   1  b  1.231064  68
10  2  a -0.979462  73
11  2  b  0.322454  97)

      

        
        
        
      

    

Finally, I calculate the average of the column M

in klmn0

, grouped by the value in the column L

:

In [19]: m0 = klmn0.groupby('L')['M'].mean(); m0
Out[19]: 
L
a   -0.307671
b    0.451144
Name: M

      

        
        
        
      

    

Now, my question is, how can I subtract m0

from a M

subframe column klmn1

given the value in the column L

? (By this means that it m0['a']

is subtracted from M

each row 's column klmn1

, which has 'a'

in the column L

as well as for m0['b']

.)

You can imagine this to replace the values ​​in a column M

klmn1

with new values ​​(after subtracting the value from m0

). Alternatively, one could do it this way to leave klmn1

unchanged and instead create a new dataframe klmn11

with the updated column M

. I am interested in both approaches.