Changing a variable into a factor variable

Question

I have a variable (year) which is all 2007 and 2008s but I need to change it into a factor so it reads 0 and 1s. Is there a way to do this?

So it can be used in a general linear model

Possible duplicate of [How to create dummy variables?](https://stackoverflow.com/questions/12758075/how-to-create-dummy-variables) — NelsonGon, Mar 23 '19 at 12:52
Ok, edit your question as shown [here](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). — NelsonGon, Mar 23 '19 at 13:14
Does `df$year <- ifelse(df$year == 2008, 1, 0)` well for you. — Sonny, Mar 23 '19 at 13:33
@Sonny thanks you very much, just so i know.. how do i undo this command? — Alex Morgan, Mar 23 '19 at 13:55
You could store the 1/0 in a different column if you want `year` column to exist as it is — Sonny, Mar 23 '19 at 14:00
@Sonny i need to run some diagnostic tests on the year data so is there a way of briefly changing it back to 2007s and 2008s? — Alex Morgan, Mar 23 '19 at 14:02

score 0 · Answer 1 · answered Mar 23 '19 at 13:57

0

Assuming there are only two years in your year variable, for example: c(2007, 2007, 2008, 2007, 2008), then:

year_as_factor <- factor(year, labels = c(0, 1))

will give you a vector of factors with values of 0 where year has 2007 and 1 where year has 2008.

answered Mar 23 '19 at 13:57

Jim Tyhurst

1

Hi Jim, thank you very much for this. Very useful. How do I recode it so it returns back to the way it was. – Alex Morgan Mar 23 '19 at 14:11
Alex, you can use `levels(year_as_factor) <- c(2007, 2008)` to change back to the original. – ags29 Mar 23 '19 at 14:16

score 0 · Answer 2 · answered Mar 23 '19 at 14:11

You don't actually need to change the levels to use it as input into a glm model, casting it as a factor using factor(year) would be sufficient. If, however, you still want to change the levels you can do so as per the answer below. In general you can change the levels of a factor variable via a statement such as

levels(year) <- c(...)

where c(...) contains the new factor levels.

Changing a variable into a factor variable

2 Answers2