Generating a variable that takes value 1 if other characteristics of other variables are fulfilled

[Michela Gasperini]

Hi I have to generate a dummy variable X1 that takes the value of 1 if only ONE of the dummy variables A B and C have value of 1, and a variable X2 if only TWO of the variables A B and C take value of 1. Do you know an easy way to do that? Thank you in advance.

[Andrew Musau]

egen X= rowtotal(A B C)
gen X1= X==1
gen X2= X==2