Split columns in dataframe with NA

Question

I have a df like this:

df <- data.frame(FOO = c(\'A|B|C\', \'A|B\', \'B|C\', \'A\', \'C\'))

> df
    FOO
1 A|B|C
2   A|B
3   B|C
4     A
5            


        

Answer 1

Use unique and strsplit to find all unique values (A, B and C in this case). Use grep to search for the unique values, and return the values when there's a match or character(0) otherwise. cbind the resulting characters. Use apply and ifelse to replace character(0) with NA.

vals <- unique(unlist(sapply(a1, function(x) strsplit(x, '|', fixed = T))))

out <- NULL
for(i in vals){
  out <- cbind(out, as.character((lapply(df$FOO, function(x) grep(x, i, value=T)))))
}

apply(out, 2, function(x) ifelse(x=="character(0)", NA, x))

     [,1] [,2] [,3]
[1,] "A"  "B"  "C" 
[2,] "A"  "B"  NA  
[3,] NA   "B"  "C" 
[4,] "A"  NA   NA  
[5,] NA   NA   "C"