Strange behaviour when piping to return() in R function?

问题

Under certain circumstances, piping to return() doesn't appear to behave expectedly. To demonstrate, here are 4 cases

Suppose we define a function that returns the result of str_replace_all

library(stringr)
library(dplyr)

string <- letters[1:9] %>% paste0(collapse="")

funct <- function(string) {
  
  return(string %>% str_replace_all(., "ef", "HHH"))
  
}

funct(string)
# [1] "abcdHHHghi"

Now suppose we pipe to return - function works as expected

funct <- function(string) {
  
  string %>% str_replace_all(., "ef", "HHH") %>% return(.)
  
}

funct(string)
# [1] "abcdHHHghi"

But if we add some arbitrary commands after the return, we do not get the expected output ([1] "abcdHHHghi")

funct <- function(string) {
  
  string %>% str_replace_all(., "ef", "HHH") %>% return(.)
  
  print('hi')
  
}

funct(string)
# [1] "hi"

Note that if we don't pipe to return, we do see the expected behaviour

funct <- function(string) {
  
  return(string %>% str_replace_all(., "ef", "HHH"))
  
  print('hi')
}

funct(string)
# [1] "abcdHHHghi"

Question

What is causing this behaviour and how do we get return to return (as expected) when piped to?

Desired Output

funct <- function(string) {

  string %>% str_replace_all(., "ef", "HHH") %>% return(.)

  print('hi')

}

funct(string)

should return # [1] "abcdHHHghi"

Note

Based on similarly strange behaviour when piping to ls(), I tried

funct <- function(string) {
  
  string %>% str_replace_all(., "ef", "HHH") %>% return(., envir = .GlobalEnv)
  
  print('hi')
  
}

funct(string)

but it did not help:

Error in return(., envir = .GlobalEnv) : 
multi-argument returns are not permitted

回答1:

return faces some evaluation issue when it is on RHS of the chain. See this github issue thread.

If you have to use return the safest way is to use

funct <- function(string) {
   return(string %>% stringr::str_replace_all("ef", "HHH"))
   print('hi')
}

funct(string)
#[1] "abcdHHHghi"

回答2:

We can use the OP's mentioned way

funct <- function(string) {

  return(string %>% string::str_replace_all(., "ef", "HHH"))

  print('hi')
 }

来源：https://stackoverflow.com/questions/59596950/strange-behaviour-when-piping-to-return-in-r-function

标签

dplyr

magrittr