I have data that I read into a dataframe specifying colClasses, e.g.:

dat <- read.table(textConnection("
One Two
D 1
B 2
A 3
C 4
"), header = TRUE, colClasses = c("factor", "integer"))

If levels aren’t specified, R orders them alphabetically:

str(dat)
'data.frame':   4 obs. of  2 variables:
 $ One: Factor w/ 4 levels "A","B","C","D": 4 2 1 3
 $ Two: int  1 2 3 4

If I want the levels to be in a different order, for example in the order the values appear –

 $ One: Factor w/ 4 levels "D","B","A","C": 1 2 3 4

– how can I specify this in the command that reads in the data?

I do not want to reorder the levels!!

I do not want to do:

dat$One <- factor(dat$One, levels = c("D","B","A","C"))