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How to sum a variable by factor levels in R?
We can do this by using aggregate function or with the help tapply
Example
> x <- data.frame(Category=factor(c("Graduation", "Graduation", "Post-Graduation", "Graduation","PhD", "Post-Graduation", "PhD")), Frequency=c(12,19,15,20,25,13,14)) > x Category Frequency 1 Graduation 12 2 Graduation 19 3 Post-Graduation 15 4 Graduation 20 5 PhD 25 6 Post-Graduation 13 7 PhD 14
Using aggregate
> aggregate(x$Frequency, by=list(Group=x$Category), FUN=sum) Group x 1 Graduation 51 2 PhD 39 3 Post-Graduation 28 Using tapply > tapply(x$Frequency, x$Category, FUN=sum) Graduation PhD Post-Graduation 51 39 28
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