Assigning a range of values to a descriptive variable in R - r

Question

Apologies in advance - I am relatively new to R/RStudio and am trying to figure out how to assign a value of ranges to a letter grade. In the project I am working on I am trying to predict a hidden value, and one portion of it derives from the three semi-revealed values represented by letter grades. For example, I may know that the three traits revealed are an A, B+, and B but not the exact numbers. However, from the previous data I have pulled, I know the following ranges are correct for each letter grade:
A+: 90 or greater
A: 86-89
A-: 82-85
B+: 82-77
B: 75-78
B-: 72-74
C+:69-71
C: 68-66
C-: 63-65
D: 60-62
F: 0-59
Is there a way for me to link these associated values to the letter grades to use later on in a multiple regression model?
Appreciate it.

Answer 1

I think you just want to organize all these values in a dataframe. Like this:
grades <- c("A+", "A", "A-", "B+", "B", "B-", "C+", "C", "C-", "D", "F")
min_value <- c(90, 86, 82, 79, 75, 72, 69, 66, 63, 60, 0)
max_value <- c(100, 89, 85, 81, 77, 74, 71, 68, 65, 62, 59)
mean_value <- (max_value+min_value)/2
df <- data.frame(grades, min_value, max_value, mean_value)
df

Answer 2

Edit: I'm no longer sure I understood your goal correctly. Here are two options to convert numeric grades to letter grades.
First, use the data.table package and perform a "rolling join". You can learn about rolling joins in this blog post:
https://r-norberg.blogspot.com/2016/06/understanding-datatable-rolling-joins.html
library(data.table)
grades =
"let, num
A+, 90
A, 86
A-, 82
B+, 80
B, 75
B-, 72
C+, 69
C, 68
C-, 63
D, 60
F, 0"
grades = read.csv(text=grades)
students =
"name, result
john, 60
mary, 86
anish, 79"
students = read.csv(text=students)
setDT(students)
setDT(grades)
grades[students, roll=TRUE, on=c("num"="result")]
#> let num name
#> 1: D 60 john
#> 2: A 86 mary
#> 3: B 79 anish
Alternatively, you could write a conversion function with a for loop. That would look something like this:
pct2let = function(grades, slack_fail = 2, slack_pass = 1){
bareme = structure(list(lb = c(90, 85, 80, 77, 73, 70, 65, 60, 57, 54,
50, 35, 0.01, 0), ub = c(100, 89.99, 84.99, 79.99, 76.99, 72.99,
69.99, 64.99, 59.99, 56.99, 53.99, 49.99, 34.99, 0.01), let = c("A+",
"A", "A-", "B+", "B", "B-", "C+", "C", "C-", "D+", "D", "E",
"F", "F*")), .Names = c("lb", "ub", "let"), class = "data.frame", row.names = c(NA,
-14L))
grades = ifelse(grades < 50, grades + slack_fail, grades + slack_pass)
out = grades
for(i in nrow(bareme):1){
out[grades >= bareme$lb[i]] = bareme$let[i]
}
return(out)
}
pct2let(c(45, 65, 78))
#> [1] "E" "C+" "B+"