R help - Oct 2013 - Passing multiple object names to a user-defined R fn XXXX

Hi all,

I am attempting to write an R fn that will accept multiple (but varying on
how many) objects (usually data frames) as inputs and return summary output.

What is the best way to pass the object names to the fn (I have thought of
2 options below) AND how do I then use the names inside the fn to reference
the actual object (I assume that I would need something like get(x[1]) for
example to have "d1" resolve the the object d1. Correct?

The 1st option I thought of was to pass the object names as a character
vector in the call to the fn:

set.matrix<-df.set(c("d1","d2","d3","d4","d5","d6","d7","d8"),by="ID")
2nd option: Is something like this possible:

set.matrix<-df.set(c(d1,d2,d3,d4,d5,d6,d7,d8),by="ID")

	[[alternative HTML version deleted]]

Hi

I will not answer your question directly but instead I have some recommendation
for you. If you can put these data frames to one list object when you creates
them, you can save yourself a lot of troubles.

some.list<-vector("list", n)
for (i in 1:n) {
some.list[[i]] <- some extensive computation or reading files
}

then you can use lapply/sapply/for cycle to make any computation directly on
list.

I use R for more than 10 years and I do not remember any situation when I would
need to create multiple objects in "n1":"nx" naming manner.

Regards
Petr

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Dan Abner
> Sent: Monday, October 14, 2013 5:10 PM
> To: r-help at r-project.org
> Subject: [R] Passing multiple object names to a user-defined R fn XXXX
> 
> Hi all,
> 
> I am attempting to write an R fn that will accept multiple (but varying
> on how many) objects (usually data frames) as inputs and return summary
> output.
> 
> What is the best way to pass the object names to the fn (I have thought
> of
> 2 options below) AND how do I then use the names inside the fn to
> reference the actual object (I assume that I would need something like
> get(x[1]) for example to have "d1" resolve the the object d1.
Correct?
> 
> The 1st option I thought of was to pass the object names as a character
> vector in the call to the fn:
> 
>
set.matrix<-df.set(c("d1","d2","d3","d4","d5","d6","d7","d8"),by="ID")
> 2nd option: Is something like this possible:
> 
> set.matrix<-df.set(c(d1,d2,d3,d4,d5,d6,d7,d8),by="ID")
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

Hello,

You should put all those data frames in a list and then use the list 
(just one object).
But if you have several objects in your workspace and need to write a 
function that accepts a varying number of arguments, use the dots argument:

df.set <- function(..., by){
	dots <- list(...)  # all those objects in a list
	for(d in dots)
		print(summary(d))
	invisible(NULL)
}

d1 <- data.frame(x = 1:4, y = 5:8)
d2 <- data.frame(a = 1:10, b = 11:20)

df.set(d1, d2)


Note that I don't use c(d1, d2), it will give something completely 
different. c() has unwanted side effects. Try it.


Hope this helps,

Rui Barradas

Em 14-10-2013 16:09, Dan Abner escreveu:
> Hi all,
>
> I am attempting to write an R fn that will accept multiple (but varying on
> how many) objects (usually data frames) as inputs and return summary
output.
>
> What is the best way to pass the object names to the fn (I have thought of
> 2 options below) AND how do I then use the names inside the fn to reference
> the actual object (I assume that I would need something like get(x[1]) for
> example to have "d1" resolve the the object d1. Correct?
>
> The 1st option I thought of was to pass the object names as a character
> vector in the call to the fn:
>
>
set.matrix<-df.set(c("d1","d2","d3","d4","d5","d6","d7","d8"),by="ID")
> 2nd option: Is something like this possible:
>
> set.matrix<-df.set(c(d1,d2,d3,d4,d5,d6,d7,d8),by="ID")
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>