如果仅在包的描述中导入foreach，如何使用％dopar％

Question

How to avoid "could not find function "%dopar%"" in a function of a package when only imports (not depends) foreach in DESCRIPTION of a package? is there a way like foreach::%dopar% as I use foreach::foreach in function? Thank you.

Code like:

In function

foreach::foreach(1:9) %dopar% {

...}

In DESCRIPTION

Imports: 
    Matrix,
    parallel,
    foreach,
   doParallel

Answer 1

The following worked for me. Define a local %do% or %dopar% as follows

`%dopar%` <- foreach::`%dopar%`
`%do%` <- foreach::`%do%`

Then you should be able to run

foreach::foreach(i = 1:9, .combine = "+") %dopar% {i}
foreach::foreach(i = 1:9, .combine = "+") %do% {i}

Answer 2

你需要使用反引号： foreach::`%dopar%` （或引号foreach::"%dopar%"也可以使用）。

Answer 3

@Kevin Zen,

I was having the same issue, but I think I just resolved it by using the "importFrom" field in the namespace file. I use Roxygen2 to document, so I simply included the tag:

#' @importFrom foreach %dopar%

with the function foreach is called in. It created a field in the namespace file like such:

importFrom(foreach,"%dopar%")

so if you aren't using Roxygen2, you could just put that line in your namespace and that should do the trick as well.

That should prevent the cran check from complaining. However, once you try to run the code on a computer that doesn't already have the "foreach" package loaded and attached via:

library(foreach)

you will get a message that %dopar% is not found if "foreach" is listed under "Imports" rather than "Depends" in your DESCRIPTION file. So make sure foreach is listed in the "Depends" field.