python pandas operations on columns

Question

Hi I would like to know the best way to do operations on columns in python using pandas.

I have a classical database which I have loaded as a dataframe, and I often have

Answer 1

Start with..

df = pd.DataFrame({'a':randrange(1,10),'b':randrange(10,20),'c':np.random.randn(10)})
a   b   c
0   7   12  0.475248
1   7   12  -1.090855
2   7   12  -1.227489
3   7   12  0.163929

end with...

df.ix[df.A < 1,df.A = df['c'] - df['d']]; df
    a   b   c
0   7   12  5.000000
1   7   12  5.000000
2   7   12  5.000000
3   7   12  5.000000
4   7   12  1.813233