Common functions that don't behave as expected with magrittr pipe?

Question

There are some cases where the magrittr pipe (%>%) doesn't behave quite as may be expected, and that therefore take a little time to debug, generate reprex's, discuss, and eventually refactor.

E.g.

• piping to ls() and
• piping to return()

Question

In the interest of proactively educating oneself, is there some compilation of known base (and perhaps tidy) R functions with which the pipe doesn't behave as one may expect?

Current solutions

• We can periodically read the magrittr issues (and probably issues with other related tidy packages), and
• Read relevant stack overflow questions.

Although these sources are somewhat disparate.

Is there a way to generate a list, or perhaps one is maintained somewhere, perhaps in documentation, on github, or elsewhere, so that it can be periodically reviewed?

Answer 1

There isn’t a way to generate such a list automatically, since you effectively need to know the semantics of a function to know why (and therefore whether) it would work inside a pipeline.

As a heuristic, any function that takes an envir parameter that’s set to a default (as in the case of ls, bit also get, exists, etc.) will behave oddly with pipes.

That said, if you understand how function evaluation works in R it is usually pretty obvious for most functions whether they will work. I therefore suggest reading up on the R model of evaluation. In particular, read the relevant chapters in Hadley Wickham’s Advanced R:

• Chapter 6 Functions
• Chapter 7 Environments

And, potentially, parts of

• Part IV Metaprogramming

To be fair, that’s a lot of material. But having a good handle of how function evaluation and scoping (environments) work in R is crucial for a solid understanding of R anyway. Metaprogramming is more advanced and it’s more important to be aware of its existence than to immediately have a solid understanding of it.