How to implement sql coalesce in pandas

Question

I have a data frame like

df = pd.DataFrame({\"A\":[1,2,np.nan],\"B\":[np.nan,10,np.nan], \"C\":[5,10,7]})
     A     B   C
0  1.0   NaN   5
1  2.0  10.0  10         


        

Answer 1

Another way is to explicitly fill column D with A,B,C in that order.

df['D'] = np.nan
df['D'] = df.D.fillna(df.A).fillna(df.B).fillna(df.C)