R function to process multiple expressions

Question

I'm trying to create a function that can evaluate multiple independent expressions. My goal is to input many expressions at once like myfunction(x = 2, y = c(5,10,11) , z = 10, ...), and use each expression's name and value to feed other functions inside of it. The transform() function works kind of like that: transform(someData, x = x*2, y = y + 1).

I know I can get the name and the value of an expression using:

> names(expression(x=2)) [1] "x" > eval(expression(x=2)) [1] 2

However, I don't know how to pass those expressions through a function. Here is some of my work so far.

With unquoted expression (x=2) I could not pass it using the dots (...).

> myfunction <- function(...) { names(expression(...)) } > myfunction(x=2) expression(...)

Now, using quotes. It gets the value but not the name. Parse structure is different from the tradicional expression. See class(expression(x=2)) and class(parse(text="x=2")), then str(expression(x=2)) and str(parse(text="x=2")).

> myfunction <- function(...) { assign("temp",...) results <- parse(text=temp) cat(names(results)) cat(eval(results)) } > myfunction("x=2") > 2

So, any ideas?

If you ever have a function that does what you want, you can view the inside of it by looking at first 'methods' then 'getAnywhere'. For example: methods(transform); getAnywhere(transform.zoo). Here you can see the line e<-eval... where I believe it does what you want. — Jason
– Jason, Commented Nov 27, 2014 at 19:28
Thank you! I was trying to use fix(transform) instead of fix(transform.data.frame) to look inside the function. — Erick Damasceno
– Erick Damasceno, Commented Nov 27, 2014 at 19:46

MrFlick · Accepted Answer · 2014-11-27 19:29:35Z

It's unclear exactly what you want the return of your function to be. You can get the names and expressions passed to a function using

myfunction <- function(...) { x<-substitute(...()) #names(x) x } myfunction(x = 2, y = c(5,10,11) , z = 10)

Here you get a named list and each of the items is an unevaluated expression or language object that you can evaluate later if you like.

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