How to flatten R data frame that contains lists?

Question

I want to find the best \"R way\" to flatten a dataframe that looks like this:

  CAT    COUNT     TREAT
   A     1,2,3     Treat-a, Treat-b
   B     4,5              


        

Answer 1

Here is another way in base r

df<-data.frame(CAT=c("A","B"))
df$COUNT <-list(1:3,4:5)
df$TREAT <-list(paste("Treat-", letters[1:2],sep=""),paste("Treat-", letters[3:5],sep=""))

Create a helper function to do the work

f <- function(l) {
  if (!is.list(l)) return(l)
  do.call('rbind', lapply(l, function(x) `length<-`(x, max(lengths(l)))))
}

Always test your code

f(df$TREAT)

#           [,1]      [,2]      [,3]     
# [1,] "Treat-a" "Treat-b" NA       
# [2,] "Treat-c" "Treat-d" "Treat-e"

Apply it

df[] <- lapply(df, f)
df

#     CAT COUNT.1 COUNT.2 COUNT.3 TREAT.1 TREAT.2 TREAT.3
#   1   A       1       2       3 Treat-a Treat-b    
#   2   B       4       5      NA Treat-c Treat-d Treat-e