Best way to replace a lengthy ifelse structure in R

Question

I have the following data frame

df = data.frame(Code=seq(80,105,1))

I need to add another column tCode that gets calculated fr

Answer 1

Come up with a matching table and merge.

I'll do the first couple statements for brevity, hopefully you get the point:

library(data.table); setDT(df)

match_table <- 
  data.table(Code = c(89:102),
             tCode = c(rep(78, 9), 79, 79, 80, 80))

df[match.table, tCode := tCode, on = "Code"]