将 purrr::pmap 与 R 的原生 pipe 运算符一起使用

Question

One use of pmap is to deal with situations where one might want map3 , but such a function does not exist in purrr . For example:

library(tidyverse)

Z <- tibble(x = list(sample(10, size = 2), sample(10, size = 3)), 
            fn = c(max, min)) 


Z %>% 
  mutate(msg2 = map2_chr(x, fn, \(x,fn) paste(toString(x), '->', fn(x))), # for 2 args this is the way
         msgp = pmap_chr(., \(x, fn) paste(toString(x), '->', fn(x))) # but can also do this
  )

(where my examples maps a function of two parameters, so I can actually use map2 ; but think of the analogous problem with three parameters).

I would like to update my code to use the new native R pipe |> , but the following does not work:

Z |> 
  mutate(msg2 = map2_chr(x, fn, \(x,fn) paste(toString(x), '->', fn(x))), # for 2 args this is the way
         msgp = pmap_chr(_, \(x, fn) paste(toString(x), '->', fn(x))) # but this is an ERROR
  )

What are some options for using pmap with mutate and with R's native pipe operator? Or, is this one situation where it makes sense to stick to using magritte 's pipe ( %>% )?

Answer 1

It may be better to use with ..1 , ..2 as arguments. In the pmap code, the . will take the full dataset columns including the msg2 created (thus it is 3 columns instead of 2), but the lambda created had only two arguments

library(dplyr)
library(purrr)
Z  |> 
  mutate(msg2 = map2_chr(x, fn, \(x,fn)
    paste(toString(x), '->', fn(x))),
   msgp = pmap_chr(across(everything()),
    ~ paste(toString(..1), "->", match.fun(..2)(..1))))

-output

# A tibble: 2 × 4
  x         fn     msg2         msgp        
  <list>    <list> <chr>        <chr>       
1 <int [2]> <fn>   9, 3 -> 9    9, 3 -> 9   
2 <int [3]> <fn>   6, 2, 9 -> 2 6, 2, 9 -> 2

---

Or if make use of the OP's code and make slight modification to include only the x, fn columns

Z |> 
  mutate(msg2 = map2_chr(x, fn, \(x,fn) 
    paste(toString(x), '->', fn(x))), # for 2 args this is the way
         msgp = pmap_chr(across(c(x, fn)),
    \(x, fn) paste(toString(x), '->', fn(x))) # but this is not an ERROR now
  )

-output

# A tibble: 2 × 4
  x         fn     msg2         msgp        
  <list>    <list> <chr>        <chr>       
1 <int [2]> <fn>   9, 3 -> 9    9, 3 -> 9   
2 <int [3]> <fn>   6, 2, 9 -> 2 6, 2, 9 -> 2