search for: teacher_unique_id

...l columns. The ID variable I use as the index variable in tapply() has 326397 unique cases. > length(unique(qq$student_unique_id)) [1] 326397 To give a sense of what my data look like and the actual problem, consider the following: qq <- data.frame(student_unique_id = factor(c(1,1,2,2,2)), teacher_unique_id = factor(c(10,10,20,20,25))) This is a student achievement database where students occupy multiple rows in the data and the variable teacher_unique_id denotes the class the student was in. What I am doing is looking to see if the teacher is the same for each instance of the unique student ID. So,...