string - Use of switch() in R to replace vector values

Question

This should be pretty simple but even after checking all documentation and on-line examples I don't get it.

I'd like to use switch() to replace the values of a character vector.

A fake, extremely simple, reproducible example:

test<-c("He is", "She has", "He has", "She is")

Let's say I want to assign "1" to sentences including the verb "to be" and "2" to sentences including the verb "to have". The following DOES NOT work:

test<-switch(test,
                "He is"=1,
                "She is"=1,
                "He has"=2,
                "She has"=2)

Error message:

+ + + + Error in switch(test, `He is` = 1, `She is` = 1, `He has` = 2, `She has` = 2) : 
  EXPR must be a length 1 vector

I think EXPR is indeed a length 1 vector, so what's wrong?

I thought maybe R expected characters as replacements, but neither wrapping switch() into an "as.integer" nor the following work:

test<-switch(test,
                "He is"="1",
                "She is"="1",
                "He has"="2",
                "She has"="2")

Maybe it doesn't vectorize, and I should make a loop? Is that it? Would be disappointing, considering the strength of R is vectorization. Thanks in advance!

Answer 1

Here is the correct way to vectorize a function, e.g. switch:

# Data vector:
test <- c("He is",
          "She has",
          "He has",
          "She is")

# Vectorized SWITCH:
foo <- Vectorize(vectorize.args = "a",
                 FUN = function(a) {
                   switch(as.character(a),
                          "He is" = 1,
                          "She is" = 1,
                          "He has" = 2,
                          2)})

# Result:
foo(a = test)

  He is She has  He has  She is 
      1       2       2       1

I hope this helps.