CODEWITHSUNDEEP
rlistevaluation
Wakan Tanka
Wakan Tanka

Reputation: 8042

how to get variable names from list

I have list of functions which also contains one user defined function:

> fun <- function(x) {x}
> funs <- c(median, mean, fun)

Is it possible to get function names as strings from this list? My only workaround so far was to create vector which contains function names as strings:

> fun.names <- c("median", "mean", "fun")

When I want to get variable name I use to do this trick (if this is not correct correct me please) but as you can see it only work for one variable not for list:

> as.character(substitute(mean))
[1] "mean"

> as.character(substitute(funs))
[1] "funs"

Is there something that will work also for list? Is there any difference if list contains functions or data types?

EDIT: I need to pass this list of functions (plus another data) to another function. Then those functions from list will be applied to dataset. Function names are needed because if there are several functions passed in list I want to being able to determine which function was applied. So far I've been using this:

window.size   <- c(1,2,3)
combinations  <- expand.grid(window.size, c(median, mean))
combinations  <- cbind(combinations, rep(c("median","mean"), each = length(window.size)))

Upvotes: 4

Views: 219

Answers (2)

bgoldst
bgoldst

Reputation: 35314

Generally speaking, this is not possible. Consider this definition of funs:

funs <- c(median,mean,function(x) x);

In this case, there's no name associated with the user-defined function at all. There's no rule in R that says all functions must be bound to a name at any point in time.

If you want to start making some assumptions about whether and where all such lambdas are defined, then possibilities open up.

One idea is to search the closure environment of each function for an entry that matches (identically) to the function itself, and then use that name. This will incur a performance penalty due to the comparison work, but may be tolerable if you don't have to run it repetitively:

getFunNameFromClosure <- function(fun) names(which(do.call(c,eapply(environment(fun),identical,fun)))[1L]);

Demo:

fun <- function(x) x;
funs <- c(median,mean,fun);
sapply(funs,getFunNameFromClosure);
## [1] "median" "mean"   "fun"

Caveats:

1: As explained earlier, this will not work on functions that were never bound to a name. Furthermore, it will not work on functions whose closure environment does not contain a binding to the function. This could happen if the function was bound to a name in a different environment than its closure (via a return value, superassignment, or assign() call) or if its closure environment was explicitly changed.

2: It is possible to bind a function to multiple names. Thus, the name you get as a result of the eapply() search may not be the one you expect. Here's a good demonstration of this:

getFunNameFromClosure(ls); ## gets wrong name
## [1] "objects"
identical(ls,objects); ## this is why
## [1] TRUE

Upvotes: 2

marbel
marbel

Reputation: 7714

Here is a hacky approach:

funs <- list(median, mean)

fun_names = sapply(funs, function(x) {
  s = as.character(deparse(eval(x)))[[2]]
  gsub('UseMethod\\(|[[:punct:]]', '', s)
})

names(funs) <- fun_names

funs

$median
function (x, na.rm = FALSE) 
UseMethod("median")
<bytecode: 0x103252878>
<environment: namespace:stats>

$mean
function (x, ...) 
UseMethod("mean")
<bytecode: 0x103ea11b8>
<environment: namespace:base>

combinations  <- expand.grid(window.size, fun_names, c(median, mean))

Upvotes: 1

Related Questions