I have a data file with indicates pretest scores for a linguistics
experiment.  The data are in long form so for each of 33 subjects there are
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

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