Question

I want to create a new column based on 4 values in another column.

if col1=1 then col2= G;
if col1=2 then col2=H;
if col1=3 then col2=J;
if col1=4 then col2=K.

HOW DO I DO THIS IN R?
Please I need someone to help address this. I have tried if/else and ifelse but none seems to be working. Thanks

Answer 1

You have a special case of looking up values where the index are integer numbers 1:4. This means you can use vector indexing to solve your problem in one easy step.

First, create some sample data:

set.seed(1)
dat <- data.frame(col1 = sample(1:4, 10, replace = TRUE))

Next, define the lookup values, and use [ subsetting to find the desired results:

values <- c("G", "H", "J", "K")
dat$col2 <- values[dat$col1]

The results:

dat
   col1 col2
1     2    H
2     2    H
3     3    J
4     4    K
5     1    G
6     4    K
7     4    K
8     3    J
9     3    J
10    1    G

---

More generally, you can use [ subsetting combined with match to solve this kind of problem:

index <- c(1, 2, 3, 4)
values <- c("G", "H", "J", "K")
dat$col2 <- values[match(dat$col1, index)]
dat
   col1 col2
1     2    H
2     2    H
3     3    J
4     4    K
5     1    G
6     4    K
7     4    K
8     3    J
9     3    J
10    1    G