if statement - Ifelse in R with multiple categorical conditions

Question

I have a data set, dt.train2 with 1500 different observations and 130 variables. One of them is languages and it can be english, french, arabic...

I want to create a ifelse string that gives attributes 1 for english, 2 for french, 3 for spanish and 0 for anything else. I have no idea how to do it.

dt.train2[, language_string := ifelse(language == "english", 
                                      1, 
                                      ifelse(language == "french", 
                                             2, 
                                             ifelse(language == "spanish",3)]

I'm using this to run linear model about sales.

Answer 1

You're almost there with the ifelse(), you just need the final else result (and a couple missing closing parentheses).

dt.train2[, language_string := ifelse(
  language == "english", 1,
    ifelse(language == "french", 2,
      ifelse(language == "spanish", 3, 0)
    )
  )
]

---

A couple other ways you could do this:

Make a lookup table and join:

# sample data
dt = data.table(language = c("english", "french", "spanish", "arabic", "chinese", "pig latin"))


lookup = data.table(language = c("english", "french", "spanish"),
                    language_string = c(1, 2, 3))

dt2 = merge(dt, lookup, by = "language", all.x = TRUE)
dt2[is.na(language_string), language_string := 0]

The above lookup table method is probably the nicest for scalability. However, for such a small number of encodings, you could also just set each of them:

# start with the default, 0
dt[, language_string := 0 ]
# then do each of the exceptions
dt[lanuage == "english", language_string := 1]
dt[language == "french", language_string := 2]
dt[language == "spanish", language_string := 3]