Pipeable assign function for R -- does not assign anything - r

Question

I have been trying to make a pipeable assign() function for use in loops in conjunction with paste0().
However I cannot get it to actually assign anything, e.g.
assignp <- function(value, x) {
assign(x, value)
}
assignp(13, "thirteen")
print(thirteen)
returns:
Error in print(thirteen) : object 'thirteen' not found
There are no error messages, it just doesn't assign the value to the variable name specified.
Can anyone tell me what I'm doing wrong?

Answer 1

The code in the question does assign it but the assignment is to the environment (sometimes referred to as a frame) that exists within the running function so when that function exits it is lost. Try this definition instead. Note that it is important that envir be an argument to address the general situation.
assignp <- function(value, x, envir = parent.frame()) {
assign(x, value, envir)
}
Below we discuss using it from the global environment with %>%, within a function using %>% and also in both those cases using |> . Also magrittr defines a sequential pipe but not an operator for it and we show how using that can further simplify this. We also show that assignp is not really needed in the first place and we can just use assign.
Using %>%
Note that if we left out .GlobalEnv then thirteen would get injected into a temporary environment created by the pipe so it would not be accessible in the next leg of the pipe and the following would give an error.
library(magrittr)
if (exists("thirteen")) rm(thirteen)
13 %>% assignp("thirteen", .GlobalEnv) %>% { . + thirteen }
## [1] 26
thirteen
## 13
Calling from function using %>%
By passing the current environment thirteen gets defined in it rather than in any temporary environment created by the pipe. We could alternately use e <- .GlobalEnv if we wanted thirteen to be injected into the global environment.
f <- function(x) {
e <- environment()
x %>%
assignp("thirteen", e) %>%
{ . + thirteen }
}
if (exists("thirteen")) rm(thirteen)
f(13)
## [1] 26
exists("thirteen")
## [1] FALSE
Using |>
|> does not create environments so this works.
if (exists("thirteen")) rm(thirteen)
13 |> assignp("thirteen") |> (\(x) x + thirteen)()
## [1] 26
thirteen
## 13
g <- function(x) x |> assignp("thirteen") |> (\(x) x + thirteen)()
if (exists("thirteen")) rm(thirteen)
g(13)
## [1] 26
exists("thirteen")
## [1] FALSE
Using only assign
Actually we don't really need assignp at all. These all work:
if (exists("thirteen")) rm(thirteen)
13 %>% assign("thirteen", ., .GlobalEnv) %>% { . + thirteen }
f2 <- function(x) {
e <- environment()
x %>%
assign("thirteen", ., e) %>%
{ . + thirteen }
}
if (exists("thirteen")) rm(thirteen)
f2(13)
g2 <- function(x) x |> assign(x = "thirteen") |> (\(x) x + thirteen)()
if (exists("thirteen")) rm(thirteen)
g2(13)
magrittr sequential pipe
magrittr defines a sequential pipe but currently there is no operator for it; however, we can readily define one.
`%s>%` <- pipe_eager_lexical
f3 <- function(x) x %s>% assign("thirteen", .) %>% { . + thirteen }
if (exists("thirteen")) rm(thirteen)
f3(13)
## [1] 26
Update
Expanded and fixed errors.

Answer 2

By default assign assigns value in it's current scope i.e within the function in this case. Specify envir = parent.frame() in assign.
assignp <- function(value, x) {
assign(x, value, envir = parent.frame())
#You can also use .GlobalEnv to assign to global environment directly.
#assign(x, value, envir = .GlobalEnv)
}
assignp(13, "thirteen")
thirteen
#[1] 13