i am trying to do this in R. it is equivalent to the stata command rowfirst suppose i have four columns as shown below (T1, T2, T3, T4). I want to create a new column (TX) which contains for each row the first element in columns T1:T4.
ID T1 T2 T3 T4
A 0 2 4 5
B . . 6 5
C . 8...