Cleaning up factor levels (collapsing multiple levels/labels)

Question

What is the most effective (ie efficient / appropriate) way to clean up a factor containing multiple levels that need to be collapsed? That is, how to combine two or more fa

Answer 1

You may use the below function for combining/collapsing multiple factors:

combofactor <- function(pattern_vector,
         replacement_vector,
         data) {
 levels <- levels(data)
 for (i in 1:length(pattern_vector))
      levels[which(pattern_vector[i] == levels)] <-
        replacement_vector[i]
 levels(data) <- levels
  data
}

Example:

Initialize x

x <- factor(c(rep("Y",20),rep("N",20),rep("y",20),
rep("yes",20),rep("Yes",20),rep("No",20)))

Check the structure

str(x)
# Factor w/ 6 levels "N","No","y","Y",..: 4 4 4 4 4 4 4 4 4 4 ...

Use the function:

x_new <- combofactor(c("Y","N","y","yes"),c("Yes","No","Yes","Yes"),x)

Recheck the structure:

str(x_new)
# Factor w/ 2 levels "No","Yes": 2 2 2 2 2 2 2 2 2 2 ...