search for: pretestdata

...400 rows, one for each item on the test, and there is a column called ‘Correct’ that shows ‘C’ for a correct response and ‘E’ for an incorrect response. I am trying to write a formula that will create a vector that indicates the number of correct answers for each subject. The following: nrow(pretestdata[(pretestdata$Subject=="1" & pretestdata$Correct=="C"),]) gives the number of correct responses for subject 1, but I would like a vector that indicates the number correct for each of 33 subjects. Thank you sincerely for your assistance. Kevin Burnham [[alternative...