I have a data set with multiple rows per patient, where each row represents a 1-week period of time over the course of 4 months. There is a variable grade that can take on values of 1,2,or 3, and I want to detect when a single patient's grade INCREASES (1 to 2, 1 to 3, or 2 to 3) at any point (the result would be a yes/no variable). I could write a function to do it but I'm betting there is some clever functional programming I could do to make use of existing R functions. Here is a sample data set below. Thank you!
df=data.frame(patient=c(1,1,1,2,2,3,3,3,3),period=c(1,2,3,1,3,1,3,4,5),grade=c(1,1,1,2,3,1,1,2,3))
what I would want is a resulting data frame of:
data.frame(patient=c(1,2,3),grade.increase=c(0,1,1))