python calculated row in dataframe subtract
# Dataframe:
# Class math score reading score writing score
# Class 1 65 73 74
# Class 2 69 66 64
df.loc['Difference'] = df.apply(lambda x: x["Class 1"] - x["Class 2"])
# Result:
# Class math score reading score writing score
# Class 1 65 73 74
# Class 2 69 66 64
# Difference -3 7 10