Dictionary style replace multiple items

Question

I have a large data.frame of character data that I want to convert based on what is commonly called a dictionary in other languages.

Currently I am going about it li

Answer 1

We can also use dplyr::case_when

library(dplyr)

foo %>%
   mutate_all(~case_when(. == "AA" ~ "0101", 
                         . == "AC" ~ "0102", 
                         . == "AG" ~ "0103", 
                         TRUE ~ .))

#  snp1 snp2 snp3
#1 0101 0101 
#2 0103   AT   GG
#3 0101 0103   GG
#4 0101 0101   GC

It checks the condition and replaces with the corresponding value if the condition is TRUE. We can add more conditions if needed and with TRUE ~ . we keep the values as it is if none of the condition is matched. If we want to change them to NA instead we can remove the last line.

foo %>%
  mutate_all(~case_when(. == "AA" ~ "0101", 
                        . == "AC" ~ "0102", 
                        . == "AG" ~ "0103"))

#  snp1 snp2 snp3
#1 0101 0101 
#2 0103  
#3 0101 0103 
#4 0101 0101 

This will change the values to NA if none of the above condition is satisfied.

---

Another option using only base R is to create a lookup dataframe with old and new values, unlist the dataframe, match them with old values, get the corresponding new values and replace.

lookup <- data.frame(old_val = c("AA", "AC", "AG"), 
                     new_val = c("0101", "0102", "0103"))

foo[] <- lookup$new_val[match(unlist(foo), lookup$old_val)]