calculate letter grade using University of Montreal convention.R

## Source: https://fep.umontreal.ca/a-propos/enseigner-a-la-fep/pedagogie/evaluation-des-apprentissages/
num2let <- data.frame(
    seuil=c(0,.345,.495,.535,.565,.595,.645,.695,.725,.765,.795,.845,.895),
    lettre=c('F','E','D','D+','C-','C','C+','B-','B','B+','A-','A','A+'))

findlet <- function(val) {
    ## Convert numeric grade into letter grade
    if (is.na(val)) { return ("NA") }
    selseuil <- max(subset(num2let,seuil<=val)$seuil)
    return(num2let[ num2let$seuil==selseuil,'lettre'][[1]])
}