根据其他三列中的值添加一列

Question

I have a data frame ('ju') that has three columns and 230 rows. The first two columns represent a pair of objects. The third column includes one of those objects. I'd like to add the fourth column which will contain the second object from that pair, as shown below.

I wrote a code to identify the value for the forth column (loser), but it does not give me any output when I run it.

for (i in 1:230) {
  if (ju$winner[i]==ju$letter2[i]) {
    paste(ju$letter1[i])
  } else {
    paste (ju$letter2[i])
  }
}

I can not see what is wrong with the code. Also I would appreciate if you can suggest how I could create this fourth column directly into my data frame, instead of creating a separate vector and then adding it to the data frame. Thanks

Answer 1

If you want to print to console, you'll need to add:

cat(ju$letter1[i])

or

print(ju$letter1[i])

Regarding the New Column question, a possible solution (sub-optimal to use a for loop here -- See suggestion from @lab_rat_kid):

ju$NewColumn = NA
for (i in 1:230) {
  if (ju$winner[i]==ju$letter2[i]) {
    ju$NewColumn[i] <- ju$letter1[i]
  } else {
    ju$NewColumn[i] <- ju$letter2[i]
  }
}

Answer 2

This will do it without a for loop:

ju$loser <- ifelse(ju$winner %in% ju$letter1, ju$letter2, ju$letter1)

Gives:

> ju
  letter1 letter2 winner loser
1       a       c      a     c
2       c       b      b     c
3       t       j      j     t
4       r       k      k     r

Answer 3

with tidyverse:

dt <- tibble(l1 = c("a", "c", "t", "r"),
             l2 = c("c", "b", "j", "k"),
             winner = c("a", "b", "j", "k"))
dt <- dt %>% 
  mutate(looser = if_else(winner == l1, l2, l1))
(dt)