How to create a plan in a function

Question

I'd like to use a function to create a drake plan. See MWE:

plan_func <- function(param) {
  drake::drake_plan(
    myparam = param
  )
}

I would like

plan_func("a")

to give

# A tibble: 1 x 2
  target  command   
  <chr>   <expr_lst>
1 myparam "a"

but instead, it gives

> plan_func("a")
# A tibble: 1 x 2
  target  command   
  <chr>   <expr_lst>
1 myparam param

It feels like this is an NSE problem. Can someone give a friendly hint how to get this right?

My appreciation in advance!

landau · Accepted Answer · 2020-06-03T01:01:05.400

2

drake_plan() supports tidy evaluation, so you can write !!param in the plan.

library(drake)
plan_func <- function(param) {
  drake::drake_plan(
    myparam = !!param
  )
}
plan_func("a")
#> # A tibble: 1 x 2
#>   target  command   
#>   <chr>   <expr_lst>
#> 1 myparam "a"

^{Created on 2020-06-02 by the reprex package (v0.3.0)}

Trickier situations like https://github.com/ropensci/drake/issues/1251 might require you to turn off the tidy_eval and transform arguments of drake_plan().

Edit

To splice multiple arguments into a function, use triple-bang (!!!) instead of bang-bang (!!):

library(drake)

plan_func <- function(param) {
  drake_plan(
    myparam = f(!!param)
  )
}

  plan_func(c("a", "b"))
#> # A tibble: 1 x 2
#>   target  command       
#>   <chr>   <expr>        
#> 1 myparam f(c("a", "b"))

plan_func <- function(param) {
  drake_plan(
    myparam = f(!!!param)
  )
}

plan_func(c("a", "b"))
#> # A tibble: 1 x 2
#>   target  command    
#>   <chr>   <expr>     
#> 1 myparam f("a", "b")

^{Created on 2020-06-02 by the reprex package (v0.3.0)}

edited Jun 03 '20 at 01:01

answered Jun 02 '20 at 12:17

landau

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Of course it does! Thanks for your quick answer, Will. – Matthew Kuperus Heun Jun 02 '20 at 17:36
Note that if `param` is a vector (such as `c("a", "b")`), you need `myparam = c(!!param)`, else `drake::make(plan_func(c("a", "b")))` fails. – Matthew Kuperus Heun Jun 02 '20 at 19:11
What about triple-bang, e.g. !!!param? That's the unquote-splice operator. – landau Jun 02 '20 at 21:44
I had the same thought and tried triple-bang. I get `Error: Can't use "!!!" at top level.` for `drake::make(plan_func(c("a", "b")))`. – Matthew Kuperus Heun Jun 02 '20 at 22:43
Just added an edit to my answer. You still might have to enclose the parameter in another function, but `!!!` opens up more flexibility. – landau Jun 03 '20 at 01:02

How to create a plan in a function

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