Custom pipe to silence warnings

问题:

Related to this question.

I'd like to build a custom pipe %W>% that would silence warnings for one operation

library(magrittr)
data.frame(a= c(1,-1)) %W>% mutate(a=sqrt(a)) %>% cos

will be equivalent to :

w <- options()$warn
data.frame(a= c(1,-1)) %T>% {options(warn=-1)} %>%
  mutate(a=sqrt(a))    %T>% {options(warn=w)}  %>%
  cos

These two tries don't work :

`%W>%` <- function(lhs,rhs){
  w <- options()$warn
  on.exit(options(warn=w))
  options(warn=-1)
  lhs %>% rhs
}

`%W>%` <- function(lhs,rhs){
  lhs <- quo(lhs)
  rhs <- quo(rhs)
  w <- options()$warn
  on.exit(options(warn=w))
  options(warn=-1)
  (!!lhs) %>% (!!rhs)
}

How can I rlang this into something that works ?

回答1:

I think I would approach it like this, by tweaking the magrittr pipes to include this new option. This way should be pretty robust.

First we need to insert a new option into magrittr's function is_pipe by which it is determined whether a certain function is a pipe. We need it to recognise %W>%

new_is_pipe = function (pipe)
{
  identical(pipe, quote(`%>%`)) || identical(pipe, quote(`%T>%`)) ||
    identical(pipe, quote(`%W>%`)) ||
    identical(pipe, quote(`%<>%`)) || identical(pipe, quote(`%$%`))
}
assignInNamespace("is_pipe", new_is_pipe, ns="magrittr", pos="package:magrittr")
`%W>%` = magrittr::`%>%`

We also need a new helper function that checks whether the pipe being processed is a %W>%

is_W = function(pipe) identical(pipe, quote(`%W>%`))
environment(is_W) = asNamespace('magrittr')

Finally, we need to put a new branch into magrittr:::wrap_function which checks if this is a %W>% pipe. If so, it inserts options(warn = -1) and on.exit(options(warn = w) into the body of the function call.

new_wrap_function = function (body, pipe, env)
{
  w <- options()$warn
  if (magrittr:::is_tee(pipe)) {
    body <- call("{", body, quote(.))
  }
  else if (magrittr:::is_dollar(pipe)) {
    body <- substitute(with(., b), list(b = body))
  }
  else if (is_W(pipe)) {
    body <- as.call(c(as.name("{"), expression(options(warn=-1)), parse(text=paste0('on.exit(options(warn=', w, '))')), body))
  }
  eval(call("function", as.pairlist(alist(. = )), body), env, env)
}
assignInNamespace("wrap_function", new_wrap_function, ns="magrittr", pos="package:magrittr")

Testing this works:

data.frame(a= c(1,-1)) %W>% mutate(a=sqrt(a)) %>% cos
#           a
# 1 0.5403023
# 2       NaN

compared to...

data.frame(a= c(1,-1)) %>% mutate(a=sqrt(a)) %>% cos
#           a
# 1 0.5403023
# 2       NaN
# Warning message:
# In sqrt(a) : NaNs produced

回答2:

Perhaps something like this with rlang:

library(rlang)
library(magrittr)

`%W>%` <- function(lhs, rhs){
  w <- options()$warn
  on.exit(options(warn=w))
  options(warn=-1)
  lhs_quo = quo_name(enquo(lhs))
  rhs_quo = quo_name(enquo(rhs))
  pipe = paste(lhs_quo, "%>%", rhs_quo)
  return(eval_tidy(parse_quosure(pipe)))
}

data.frame(a= c(1,-1)) %W>% mutate(a=sqrt(a)) %>% cos

Result:

          a
1 0.5403023
2       NaN

Note:

• You need enquo instead of quo because you are quoting the code that was supplied to lhs and rhs, not the literals lhs and rhs.

• I couldn't figure out how to feed lhs_quo/lhs into rhs_quo (which was a quosure) before it was evaluated, neither can I evaluate rhs_quo first (throws an error saying a not found in mutate(a=sqrt(a)))

• The workaround that I came up with turns lhs and rhs into strings, pastes them with "%>%", parses the string to quosure, then finally tidy evaluates the quosure.

回答3:

I'm not sure this solution works perfectly, but it's a start:

`%W>%` <- function(lhs, rhs) {
  call <- substitute(`%>%`(lhs, rhs))
  eval(withr::with_options(c("warn" = -1), eval(call)), parent.frame())
}

This seems to work for the following 2 examples:

> data.frame(a= c(1,-1)) %W>% mutate(a=sqrt(a)) %>% cos
          a
1 0.5403023
2       NaN
> c(1,-1) %W>% sqrt()
[1]   1 NaN

回答4:

Based on @dww's answer I created a package which integrates this pipe among others :

# devtools::install_github("moodymudskipper/mmpipe")
library(mmpipe)
library(dplyr)
data.frame(a= c(1,-1)) %W>% mutate(a=sqrt(a)) %>% cos
# a
# 1 0.5403023
# 2       NaN

The package offers also a way to define easily one own's pipe operators, If we didn't already have %W>% we could do :

add_pipe(`%W2>%`, substitute(
  {options(warn = -1); on.exit(options(warn = w)); b},
  list(w = options()$warn, b = body)))

where the second argument will create the new body of the function, and the variable body is a call containing the body of the function before modification (in the following case it's quote(mutate(.a=sqrt(a)))):

data.frame(a= c(1,-1)) %W2>% mutate(a=sqrt(a)) %>% cos
# a
# 1 0.5403023
# 2       NaN

More examples in the readme of mmpipe