How to create an R function for use by NetLogo

Question

When using NetLogo's R extension, how do I create or load up an R function for use by the agents later? The following doesn't work:

extensions [r]
to setup
  r:eval "function line 1"
  r:eval "function line 2"
  r:eval "function line 3"
  etc.
end

and my function seems too long to do it all on one line (I'm not sure that would work when it got sent into R anyway). Does anyone have any advice?

Answer 1

I'd recommend building your functions in an R file then sourcing that file within NetLogo. For example, I have a file called 'example_r.R' that just serves to store Foo:

Foo <- function(value) {
  return(abs(value))
}

I can then source() the file with r:eval and all contained functions will be available:

extensions [r]

to setup
  ca
  ask n-of 5 patches [ sprout 1 ]    
  r:eval "source('C:/example_r.R')"  
  reset-ticks
end

to go 
  ask turtles [
    rt random 60 - 30
    fd 1
    r:put "xcor" xcor 
    r:eval "out <- Foo(xcor)"
    show ( word "My xcor is " round xcor " but my absolute xcor is: " round r:get "out" )
  ]
  tick
end

After setup and go:

(turtle 4): "My xcor is 7 but my absolute xcor is: 7"
(turtle 3): "My xcor is 2 but my absolute xcor is: 2"
(turtle 1): "My xcor is -3 but my absolute xcor is: 3"
(turtle 2): "My xcor is -3 but my absolute xcor is: 3"
(turtle 0): "My xcor is -15 but my absolute xcor is: 15"