R: Encode character variables into numeric

问题

In R code I have a character variable var that has values "AA", "AB", "AC", etc.

str(var)
chr [1:17003] "AA" "AA" "AA" "AA" "AB" "AB" ...

How can I convert it to numeric variable so that "AA" would be coded as, e.g. 1, "AB" - as 2, etc.

回答1:

You can convert the string to a factor and then to numeric.

x <- c("AA", "AB", "AB", "AC", "AA", "XY")
as.numeric(as.factor(x))
# [1] 1 2 2 3 1 4

Alternatively, you can use match and unique:

match(x, unique(x))
# [1] 1 2 2 3 1 4

回答2:

you can use them by directly converting them into factors with labeling.

x$Country = factor(x$Country,
               levels = c('AA', 'AB', 'AC'),
               labels = c(1, 2, 3))

来源：https://stackoverflow.com/questions/29764983/r-encode-character-variables-into-numeric