Is it possible to allow "UseMethod" to see class functions defined in other environments? See the below code for an example. I would like the h.logical to be detected too such that h(TRUE) would return "logical".
h <- function(x) {
UseMethod("h")
}
h.character <- function(x){ "char"}
h.numeric <- function(x) { "num" }
aa = list(h.logical=function(x){"logical"})
attach(aa)
h("a")
h(10)
h(TRUE)
This code now throws an error in the last line:
Error in UseMethod("h") : no applicable method for 'h' applied to an object of class "logical"
Solving the issue with this example suffices. If that is not possible, I would appreciate help solving the actual use case in another way.
The use case is as follows: I have a package with functions like h above, then I want to add a class to that function. This works fine just adding the new function to .Globalenv. The problem occurs when I want to test this using testthat as I am not allowed to write to .Globalenv within a test. Adding the new class function to some other environment within the test makes it detectable by methods(), however, UseMethod still does not see it and throws an error. Any ideas?
Can I use something else then UseMethod for this purpose or do some other hack while testing to mimic the actual usage?
Any help or pointers to how to handle this is highly appreciated!
Related
I have a bunch of functions and I'm trying to keep my workspace clean by defining them in an environment and attaching the environment. Some of the functions are S3 generics, and they don't seem to play well with this approach.
A minimum example of what I'm experiencing requires 4 files:
testfun.R
ttt.xxx <- function(object) print("x")
ttt <- function(object) UseMethod("ttt")
ttt2 <- function() {
yyy <- structure(1, class="xxx")
ttt(yyy)
}
In testfun.R I define an S3 generic ttt and a method ttt.xxx, I also define a function ttt2 calling the generic.
testenv.R
test_env <- new.env(parent=globalenv())
source("testfun.R", local=test_env)
attach(test_env)
In testenv.R I source testfun.R to an environment, which I attach.
test1.R
source("testfun.R")
ttt2()
xxx <- structure(1, class="xxx")
ttt(xxx)
test1.R sources testfun.R to the global environment. Both ttt2 and a direct function call work.
test2.R
source("testenv.R")
ttt2()
xxx <- structure(1, class="xxx")
ttt(xxx)
test2.R uses the "attach" approach. ttt2 still works (and prints "x" to the console), but the direct function call fails:
Error in UseMethod("ttt") :
no applicable method for 'ttt' applied to an object of class "xxx"
however, calling ttt and ttt.xxx without arguments show that they are known, ls(pos=2) shows they are on the search path, and sloop::s3_dispatch(ttt(xxx)) tells me it should work.
This questions is related to Confusion about UseMethod search mechanism and the link therein https://blog.thatbuthow.com/how-r-searches-and-finds-stuff/, but I cannot get my head around what is going on: why is it not working and how can I get this to work.
I've tried both R Studio and R in the shell.
UPDATE:
Based on the answers below I changed my testenv.R to:
test_env <- new.env(parent=globalenv())
source("testfun.R", local=test_env)
attach(test_env)
if (is.null(.__S3MethodsTable__.))
.__S3MethodsTable__. <- new.env(parent = baseenv())
for (func in grep(".", ls(envir = test_env), fixed = TRUE, value = TRUE))
.__S3MethodsTable__.[[func]] <- test_env[[func]]
rm(test_env, func)
... and this works (I am only using "." as an S3 dispatching separator).
It’s a little-known fact that you must use .S3method() to define methods for S3 generics inside custom environments (outside of packages).1 The reason almost nobody knows this is because it is not necessary in the global environment; but it is necessary everywhere else since R version 3.6.
There’s virtually no documentation of this change, just a technical blog post by Kurt Hornik about some of the background. Note that the blog post says the change was made in R 3.5.0; however, the actual effect you are observing — that S3 methods are no longer searched in attached environments — only started happening with R 3.6.0; before that, it was somehow not active yet.
… except just using .S3method will not fix your code, since your calling environment is the global environment. I do not understand the precise reason why this doesn’t work, and I suspect it’s due to a subtle bug in R’s S3 method lookup. In fact, using getS3method('ttt', 'xxx') does work, even though that should have the same behaviour as actual S3 method lookup.
I have found that the only way to make this work is to add the following to testenv.R:
if (is.null(.__S3MethodsTable__.)) {
.__S3MethodsTable__. <- new.env(parent = baseenv())
}
.__S3MethodsTable__.$ttt.xxx <- ttt.xxx
… in other words: supply .GlobalEnv manually with an S3 methods lookup table. Unfortunately this relies on an undocumented S3 implementation detail that might theoretically change in the future.
Alternatively, it “just works” if you use ‘box’ modules instead of source. That is, you can replace the entirety of your testenv.R by the following:
box::use(./testfun[...])
This code treats testfun.R as a local module and loads it, attaching all exported names (via the attach declaration [...]).
1 (and inside packages you need to use the equivalent S3method namespace declaration, though if you’re using ‘roxygen2’ then that’s taken care of for you)
First of all, my advice would be: don't try to reinvent R packages. They solve all the problems you say you are trying to solve, and others as well.
Secondly, I'll try to explain what went wrong in test2.R. It calls ttt on an xxx object, and ttt.xxx is on the search list, but is not found.
The problem is how the search for ttt.xxx happens. The search doesn't look for ttt.xxx in the search list, it looks for it in the environment from which ttt was called, then in an object called .__S3MethodsTable__.. I think there are two reasons for this:
First, it's a lot faster. It only needs to look in one or two places, and the table can be updated whenever a package is attached or detached, a relatively rare operation.
Second, it's more reliable. Each package has its own methods table, because two packages can use the same name for generics that have nothing to do with each other, or can use the same class names that are unrelated. So package code needs to be able to count on finding its own definitions first.
Since your call to ttt() happens at the top level, that's where R looks first for ttt.xxx(), but it's not there. Then it looks in the global .__S3MethodsTable__. (which is actually in the base environment), and it's not there either. So it fails.
There is a workaround that will make your code work. If you run
.__S3MethodsTable__. <- list2env(list(ttt.xxx = ttt.xxx))
as the last line of testenv.R, then you'll create a methods table in the global environment. (Normally there isn't one there, because that's user space, and R doesn't like putting things there unless the user asks for it.)
R will find that methods table, and will find the ttt.xxx method that it defines. I wouldn't be surprised if this breaks some other aspect of S3 dispatch, so I don't recommend doing it, but give it a try if you insist on reinventing the package system.
I know there are related posts, but with insufficient answers. So please answer seriously to this question.
There are two packages ("keithley" and "xantrex") which control two different hardware devices. Therefore, both are independent from each other. Each of them must be initialised separately. So I wrote two methods
init.keithley(inst,...) # in keythley package
and
init.xantrex(inst,...) # in xantrex package
for the generic S3 function init(inst,...). I tried to declare the generic function in the keithley package and in the xantrex package, but then it is masked, once the latter is loaded and the methods where not found any more.
What I tried is the .onAttach()-hook
.onAttach <- function(libname, pkgname)
{
if(!exists("init"))
eval(expression(init <- function(inst,...) UseMethod("init")),envir = .GlobalEnv)
}
But with this it is NOT possible to evaluate the init() function within the package namespace. This can be proofed with the option envir = environment(), which will not work. I also tried setGenericS3() and setGeneric() with always the same result.
The "dirty" solution could be to define a third package and import it, but there must be a clean way to do this.
Where and how should I define the generic function?
Here is the solution:
As I understand, an attached package has three environments (e.g. "package:Xantrex", "namespace:Xantrex" and "imports:Xantrex") the different meaning of these is explained in detail here: Advanced R.
Now, we have to test whether the generic function init() is already there and if not we have to initialize it in the right environment. The following code will do that for us.
.onAttach <- function(libname, pkgname)
{
if(!exists("init",mode = "function"))
eval(expression(init <- function(inst,...) UseMethod("init")),envir = as.environment("package:Xantrex"))
}
The .onAttach-hook, is necessary to guarantee that the different namespaces are initialized. In contrast to that the .onLoad-hook, would be too early. Mention that the expression is evaluated in the package:Xantrex environment, so the generic becomes visible in the search path.
Next to that take care, that your NAMESPACE file will export(init.xantrex) and NOT S3method(init,xantrex). The latter will result an error, because the generic for the method init.xantrex()is not present while building the package.
Best!
Martin
I am fairly new to R, so my apologies if this question is a bit silly.
I am calling a function in an external package ('mmlcr', although I don't think that is directly relevant to my problem), and one of the required inputs (data) is a data.frame. I compose the data.frame from various data using the following approach (simplified for illustration):
#id, Time, and value are vectors created elsewhere in the code.
myData = data.frame(a=id, b=Time, c=value)
out <- mmlcr( input1, input2, data=myData, input4)
Which throws the error:
Error in is.data.frame(data) : object 'myData' not found
The debugger indicates that this error is thrown during the mmlcr() call.
I then added a print(ls()) immediately prior to the mmlcr() call, and the output confirmed that "myData" was in my function workspace; further is.data.frame(myData) returned TRUE. So it seems that "myData" is successfully being created, but for some reason it is not passing into the mmlcr() function properly. (Commenting this line causes no error to be thrown, so I'm pretty sure this is the problematic line).
However, when I put the exact same code in a script (i.e., not within a function block), no such error is thrown and the output is as expected. Thus, I assume there is some scoping issue that arises.
I have tried both assignment approaches:
myData = data.frame(a=id, b=Time, c=value)
myData <- data.frame(a=id, b=Time, c=value)
and both give me the same error. I admit that I don't fully understand the scope model in R (I've read about the differences between = and <- and I think I get it, but I'm not sure).
Any advice you can offer would be appreciated.
MMLCR is now deprecated and you should search for some alternatives. Without looking too much into it, I sleuthed through an old repo and found the culprit:
m <- eval(m, data)
in the function mmlcr.default. There are a lot of reasons why this is bad, but scoping is the big one. R has this issue with the subset.data.frame function, see my old SO question. Rather than modify the source code, I would find a way to do your function with a subroutine using a for, repeat, or while loop.
I know something similar has been asked before here on SO, but the solution given there doesn't seem to apply in my case.
I'm trying to follow convention in creating a package by referring to functions exported from other namespaces and avoiding use of require() within a function.
I'm basically trying to prevent a function taking too long to run. For example,
fun <- function(i){
require(R.utils)
setTimeLimit(elapsed=10, transient=TRUE) # prevent taking more than 10secs
return(i^i)
}
>fun(10)
Works fine, but if I try:
require(R.utils)
fun <- function(i){
R.utils:::setTimeLimit(elapsed=10, transient=TRUE) # prevent taking more than 10secs
return(i^i)
}
>fun(10)
I get:
Error in get(name, envir = asNamespace(pkg), inherits = FALSE) :
object 'setTimeLimit' not found
Changing ::: to :: doesn't change this behavior.
I'm open to any simpler methods to achieving the same objective.
Also is it really so bad to have require() calls inside a function?
Many thanks!
EDIT:
If import works then great, thanks. Still in development so wanted to make sure it would be OK.
EDIT:
Apologies, it's there in base. Not sure how I missed this; I was originally using R.utils::evalWithTimeout and must have assumed both were in the same package. *looks sheepish*
I'm just posting this to prevent the question from showing up as unanswered, but will be glad to accept another...
isTRUE("setTimeLimit" %in% ls(getNamespace("base"), all.names=TRUE))
I've noticed some strange behaviour in R reference classes when trying to implement some optimisation algorithm. There seems to be some behind-the-scenes parsing magic involved in initialising methods in a particular which makes it difficult to work with anonymous functions.
Here's an example that illustrates the difficulty: I define a function to optimise (f_opt), a function that runs optim on it, and a reference class that has these two as methods. The odd behaviour will be clearer in the code
f_opt <- function(x) (t(x)%*%x)
do_optim_opt <- function(x) optim(x,f)
do_optim2_opt <- function(x)
{
f(x) #Pointless extra evaluation
optim(x,f)
}
optClass <- setRefClass("optClass",methods=list(do_optim=do_optim_opt,
do_optim2=do_optim2_opt,
f=f_opt))
oc <- optClass$new()
oc$do_optim(rep(0,2)) #Doesn't work: Error in function (par) : object 'f' not found
oc$do_optim2(rep(0,2)) #Works.
oc$do_optim(rep(0,2)) #Parsing magic has presumably happened, and now this works too.
Is it just me, or does this look like a bug to other people too?
This post in R-devel seems relevant, with workaround
do_optim_opt <- function(x, f) optim(x, .self$f)
Seems worth a post to R-devel.