[R] Functional Programming Problem Using purr and R's data.table shift function

[Rui Barradas]

Às 06:50 de 31/12/2022, Michael Lachanski escreveu:
> Hello,
> 
> I am trying to make a habit of "functionalizing" all of my code as
> recommended by Hadley Wickham. I have found it surprisingly difficult to do
> so because several intermediate features from data.table break or give
> unexpected results using purrr and its data.table adaptation, tidytable.
> Here is the a minimal working example of what has stumped me most recently:
> 
> ===
> 
> library(data.table); library(tidytable)
> 
> minimal_failing_function <- function(A){
>    DT <- data.table(A)
>    DT[ , A:= shift(A, fill = NA, type = "lag", n = 1)] %>% `[`
>    return(DT)}
> # works
> minimal_failing_function(c(1,2))
> # fails
> tidytable::pmap_dfr(.l = list(c(1,2)),
>                      .f = minimal_failing_function)
> 
> 
> ===
> These should ideally give the same output, but do not. This also fails
> using purrr::pmap_dfr rather than tidytable. I am using R 4.2.2 and I am on
> Mac OS Ventura 13.1.
> 
> Thank you for any help you can provide or general guidance.
> 
> 
> ==
> Michael Lachanski
> PhD Student in Demography and Sociology
> MA Candidate in Statistics
> University of Pennsylvania
> mikelach using sas.upenn.edu
> 
> 	[[alternative HTML version deleted]]
> 
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> and provide commented, minimal, self-contained, reproducible code.
Hello,

Use map_dfr instead of pmap_dfr.


library(data.table)
library(tidytable)

minimal_failing_function <- function(A) {
   DT <- data.table(A)
   DT[ , A:= shift(A, fill = NA, type = "lag", n = 1)] %>% `[`
   return(DT)
}

# works
tidytable::map_dfr(.x = list(c(1,2)),
                    .f = minimal_failing_function)
#> # A tidytable: 2 × 1
#>       A
#>   <dbl>
#> 1    NA
#> 2     1


Hope this helps,

Rui Barradas