Question

i want to store additional information on top of a data.frame and return it from a function. as you can see – the additional data disappears.
example :

> d<-data.frame(N1=c(1,2,3),N2=(LETTERS[1:3]))
> d
  N1 N2
1  1  A
2  2  B
3  3  C
> d.x = 3
> d
  N1 N2
1  1  A
2  2  B
3  3  C
> d.x
[1] 3
> foo1 <- function() {
+ d<-data.frame(N1=c(1,2,3),N2=(LETTERS[1:3]))
+ d.x=3
+ return(d)
+ }
> 
> d1<-foo1()
> d1
  N1 N2
1  1  A
2  2  B
3  3  C
> d1.x
Error: object 'd1.x' not found

i looked into assign but since the data.frame is created inside the function and being returned i assume that it’s not relevant here.
Thanks.

Answer 1

Your comments suggest you want to create an attribute (the usual way to attach “metadata” to objects in R) named “d.3” and use foo1 to set that attribute for a dataframe:

d <- data.frame(N1=c(1,2,3),N2=(LETTERS[1:3]))
foo1 <- function(d, attrib) {
   attr(d, "d.x") <- attrib
  return(d)
  }
d <- foo1(d, 3)  # need to assign value to 'd' since function results are not "global"
d    # note that the default print method for dataframes does not show the attributes
#---------
  N1 N2
1  1  A
2  2  B
3  3  C
#-----
 attributes(d)
#-----

$names
[1] "N1" "N2"

$row.names
[1] 1 2 3

$class
[1] "data.frame"

$d.x
[1] 3

See ?attr and ?attributes for more specifics. There is also a comments function.