asjohnson asjohnson - 1 month ago 10
R Question

Grouping 2 levels of a factor in R

I have a column of data that is a factor with levels A, B and C, I am interested in combining two of these levels into one factor, so it would become A and B, with B = B and C, or maybe a new variable A and D, with D = B and C. I can come up with plenty of ways to do this by looping through the column with if statements, but I feel like there should be a more elegant approach and I was wondering if someone could point me in the right direction.

Thanks as always SO.

Answer

Use levels(x) <- ... to specify new levels, and to combine some previous levels. For example:

f <- factor(LETTERS[c(1:3, 3:1)])
f
[1] A B C C B A
Levels: A B C

Now combine "A" and "B" into a single level:

levels(f) <- c("A", "A", "C")
f
[1] A A C C A A
Levels: A C
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