Unpacking argument lists for ellipsis in R

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I am confused by the use of the ellipsis (...) in some functions, i.e. how to pass an object containing the arguments as a single argument.

In Python it is called "unpacking argument lists", e.g.

>>> range(3, 6)             # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> range(*args)            # call with arguments unpacked from a list
[3, 4, 5]

In R for instance you have the function file.path(...) that uses an ellipsis. I would like to have this behaviour:

> args <- c('baz', 'foob') 
> file.path('/foo/bar/', args)
[1] 'foo/bar/baz/foob'

Instead, I get

[1] 'foo/bar/baz' 'foo/bar/foob'

where the elements of args are not "unpacked" and evaluated at the same time. Is there a R equivalent to Pythons *arg?

The syntax is not as beautiful, but this does the trick:

do.call(file.path,as.list(c("/foo/bar",args)))

do.call takes two arguments: a function and a list of arguments to call that function with.

The Mysterious Ellipsis: Tutorial, So make sure you're always unpacking the ellipsis content using the list() function print(paste("Number of ellipsis-arguments:", length(list(. R functions: passing arguments with ellipsis. Ask Question Asked 3 years, 1 month ago. Unpacking argument lists for ellipsis in R. 726. data.table vs dplyr: can

You can extract information from the ellipsis by calling list(...) inside the function. In this case, the info in the ellipsis is packaged as a list object. For example:

> foo <- function(x,...){
+   print(list(...))
+ }
> foo(1:10,bar = 'bar','foobar')
$bar
[1] "bar"

[[2]]
[1] "foobar"

You can achieve the desired behaviour from vectorised functions like file.path with a call to do.call, which is sometimes simpler to use with the wrapper splat (in the plyr package)

> args <- c('baz', 'foob')
> library(plyr)
> splat(file.path)(c('/foo/bar', args))
[1] "/foo/bar/baz/foob"

A new R trick … for me at least, Specifically, how to unpack and prepare them in R using , list(), and .com/​questions/3414078/unpacking-argument-lists-for-ellipsis-in-r. The former point is strength and quirk of R, as it allows for arguments encapsulated in to be passed on to additional functions: f = function(x, ) {. y = g(x, ) return(y) } The latter point above (unpacking ) is actually easy to do: f = function(x, ) {.

It took me a while to find it, but the purrr package has an equivalent to plyr::splat: it's called lift_dl.

The "dl" in the name stands for "dots to list", as it's part of a series of lift_xy functions that can be used to "lift" the domain of a function from one kind of input to another kind, these "kinds" being lists, vectors and "dots".

Since lift_dl is probably the most useful of those, there is a simple lift alias provided for it.

To reuse the above example:

> library(purrr)
> args <- c('baz', 'foob')
> lift(file.path)(c('/foo/bar', args))
[1] "/foo/bar/baz/foob"

Functions, Functions are one of the fundamental building blocks of the R language. mean​() function; or it could be a list, as in the output of many statistical tests or models. unpack the appropriate arguments from the # ellipses. mad_libs <- function(. # ellipses as an argument in a function. Below I have an example function that Below I have an example function that # is supposed to add two explicitly named arguments called alpha and beta.

The three-dots construct in R, Technically it is ellipsis, but more commonly called “…”, dots, dot-dot-dot or args(apply) function (X, MARGIN, FUN, ) NULL. This has the  If you have used R before, then you surely have come across the three dots, e.g. print(x, ) In technical language, this is called an ellipsis. And it means that the function is designed to take any number of named or unnamed arguments. By the way, the ellipsis is not a specialty of R. Other programming languages have the same or a similar concept.

Swirl R Programming Script Answers · GitHub, # Do your argument unpacking here! args <- list() place <-  Since our tuples are immutable, you can convert the args tuple to a list so you can also modify, delete and re-arrange items in i. Packing and Unpacking Below is an example that shows both packing and unpacking.

5.2 – Variable Number of Arguments, Besides those arguments, the arg table has an extra field, n , with the actual number of arguments collected. Sometimes, a function has some fixed parameters  To package a programmatically generated argument list one uses the do.call() function: result = do. call ('fun', list (arg1, arg2, etc, etc)) where the first argument is the name of the function to call, and the second argument is a list of arguments to pass along. For all intents and purposes, the R statement above is equivalent to the Matlab

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