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.