Create new column based on 4 values in another column

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 could use nested ifelse:

col2 <- ifelse(col1==1, "G",         ifelse(col1==2, "H",         ifelse(col1==3, "J",         ifelse(col1==4, "K",                         NA  )))) # all other values map to NA 

In this simple case it's overkill, but for more complicated ones...

Answer 2

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 

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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