df.mean()   # Performing a descriptive statistic for columns(variables)
df.mean(1)  # operation on the other axis  
s = pd.Series([1,3,5,np.nan,6,8], index=dates).shift(2) # Operating with objects that have different dimensionality and need alignment. In addition, pandas automatically broadcasts along the specified dimension.
df.sub(s, axis='index') #