I have the following data frame:
df <- data.frame(
item=c("a","","a","d","e"),
price_today=c(1,2,"THREE%%",4,"SIX/SIX"))
If I would like to select "THREE%%" and "SIX/SIX" in column price_today
and convert them to "3?3" and "6?6", respectively, how should I go about it?