R: Simplifying code to convert letter grades to numeric grades

Question

I have written a function in R that will convert a data frame containing letter grades into numeric grades. I then use sapply() on each column of the data frame. Is there a

Answer 1

First vectorize your function: you could do this with ifelse, or:

grvec <- c("A+"=4.3,"A"=4,"A-"=3.7,"B+"=3.3,"B"=3,"B-"=2.7,
           "C+"=2.3,"C"=2,"C-"=1.7,"D+"=1.3,"D"=1,"D-"= 0.7,
       "F"=0)

grades <- data.frame(final_exam=c("C","C-","D+"),
                     quiz_avg=c("A","B-","Q"))

##   final_exam quiz_avg
## 1          C        A
## 2         C-       B-
## 3         D+        Q

num_grades <- apply(grades,2,function(x) grvec[as.character(x)])
##      final_exam quiz_avg
## [1,]        2.0      4.0
## [2,]        1.7      2.7
## [3,]        1.3       NA