In R, can I pass arguments of the parameter from a variable (only if that variable exists)?

Question

I am creating a shiny app where the user passes some inputs in the app. Based on those inputs, I am trying to pass arguments to the function called 'cohort()'. However, I am encountering issues in passing the arguments to the cohort() function. Here is the relevant portion of my code:

This code loops to create multiple variables based on user inputs.

library(Capr)

for (i in seq(2)){
assign(paste0('ad_cr',i),atLeast(1L, 
query = condition(cs(descendants(i)))))
}

Let's assume that 2 variables were created -> ad_cr1 and ad_cr2.

Function when the no variables were generated:

library(Capr)
cd <- cohort(entry = condition(cs(100)),
         attrition = attrition(),
exit = exit(
  endStrategy = observationExit()
))

I am trying to pass the values of ad_cr1 and ad_cr2 to the cohort() function within the attrition argument. However, I am not sure how to do this. How can I modify my code to achieve this?

Function when the two variables were generated:

cd <- cohort(entry = condition(cs(100)),
         attrition = attrition(
                   'ad_cr1' = withAll(ad_cr1),
                   'ad_cr2' = withAll(ad_cr2)),
exit = exit(
  endStrategy = observationExit()
))

It's easier to help you if you include a simple [reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) with sample input and desired output that can be used to test and verify possible solutions. — MrFlick, Jun 15 '23 at 20:38

score 0 · Accepted Answer · answered Jun 16 '23 at 09:07

Avoid local variables, by keeping variables together in a list; this list can be passed off to other functions like attrition() ; finally I wrapped it all up in a function you can call.

library(Capr)
library(purrr)

cohort_builder <- function(sequence, prefix) {
  assign_names <- paste0(prefix, sequence)
  assignations <- map(
    sequence,
    \(x)atLeast(1L,
      query = condition(cs(descendants(x)))
    )
  ) |> set_names(assign_names)


  cohort(
    entry = condition(cs(100)),
    attrition = do.call(
      attrition,
      map(assignations, \(x){
        withAll(x)
      })
    ),
    exit = exit(
      endStrategy = observationExit()
    )
  )
}

my_empty <- cohort_builder(sequence = NULL, prefix = NULL)
my_2 <- cohort_builder(sequence = seq(2), prefix = "ad_cr")

In R, can I pass arguments of the parameter from a variable (only if that variable exists)?

1 Answers1