How to convert from category to numeric in r

Question

Here is my problem:

I have a table with categories and I want to rank them:

category
dog
cat
fish
dog
dog

What I want is to add

Answer 1

Hopefully category is a factor variable. If not, convert it to factor:

category <- as.factor(category)

You could use the relevel function to assigned level 1 to the category "dog" as follows:

levels(category) <- relevel(category, ref = "dog")

and then create a data frame using following code:

df <- data.frame(category,as.numeric(category))
colnames(df) <- c("category","rank")

as.numeric function returns the levels of the factors which is the rank in your case.