How do I pass a vector as a parameter in a switch statement

Question

My googling of the question didn't return helpful results and the documentation for ?switch doesn't tell me how so I'm hoping I can get this answered here.

Say I have a vector:

cases<- c("one","two","three")

and I want to use a switch statement with those elements as the parameters for the switch statement:

switch(input,cases)

The above will only output anything if input=1 in which case it will output:

switch(1,cases)
# [1] "one" "two" "three"

Any other parameter will not return anything. The only way I can get the desired behavior is if I explicitly type the cases in the switch statement as such:

switch(2,"one","two","three")
# [1] "two"

I want the behavior where I can pass a list/vector/whatever as a parameter in switch() and achieve the following behavior:

switch(2,cases)
# [1] "two"

Answer 1

The switch function takes an expression indicating which argument number to select from the remaining arguments to the function. As you note, this means you would need to split up your vector into separate arguments when invoking switch. You could achieve this by converting your vector to a list with as.list and then passing each list element as separate arguments to switch with do.call:

do.call(switch, c(1, as.list(cases)))
# [1] "one"
do.call(switch, c(2, as.list(cases)))
# [1] "two"
do.call(switch, c(3, as.list(cases)))
# [1] "three"

I don't really see the benefit of doing this over using simple vector indexing:

cases[1]
# [1] "one"
cases[2]
# [1] "two"
cases[3]
# [1] "three"