Make new column in Panda dataframe by adding values from other columns

Question

I have a dataframe with values like

A B 1 4 2 6 3 9 

I need to add a new column by adding values from column A and B, like

A B C 1 4 5 2 6 8 3 9 12 

I believe this can be done using lambda function, but I can't figure out how to do it.

Answer 1

Very simple:

df['C'] = df['A'] + df['B'] 

Answer 2

Building a little more on Anton's answer, you can add all the columns like this:

df['sum'] = df[list(df.columns)].sum(axis=1)