R, assign content from .rda object with load()

Question

This is very basic (and I suspect this has been asked elsewhere, although not quite here ).

I have a huge number of .rda files each with a single data frame. I would like to do calculations on each data frame and hence need loading them (load()). Had they been .RDS object I would something like:

#My data
x <- data.frame(a=1:3)
y <- data.frame(a=3:6)

#Save as RDS 
saveRDS(x, file = "x.rds")
saveRDS(y, file = "y.rds")

files <- c("x.rds", "y.rds")
data <- lapply(files, readRDS)

#Do something with the data in the list "data"

How can I do a similar thing using load since this you cannot assign the data - only the name - to a variable:

x <- data.frame(a=1:3)

> x
  a
1 1
2 2
3 3

save(x, file= "x.rda")
x <- load("x.rda")

> x
[1] "x"

score 5 · Accepted Answer · answered Jan 21 '16 at 14:52

If you are certain that all of your files only contain a single object, you could take advantage of the envir argument of load in a wrapper function like this:

load_object <- function(file) {
  tmp <- new.env()
  load(file = file, envir = tmp)
  tmp[[ls(tmp)[1]]]
}

Usage would be as follows:

not_x <- data.frame(xx = 1:5)
save(not_x, file = "~/tmp/x.Rdata") 

(x <- load_object("~/tmp/x.Rdata"))
#  xx
#1  1
#2  2
#3  3
#4  4
#5  5

all.equal(not_x, x)
#[1] TRUE

score 1 · Answer 2 · answered Jan 21 '16 at 14:44

You want to make use of the base get function with something like:

> # My data
> x <- data.frame(a=1:3)
> y <- data.frame(a=4:6)

> # Save as RDA 
> save(x, file = "x.rda")
> save(y, file = "y.rda")

> files <- c("x.rda", "y.rda")
> data <- lapply(lapply(files, load), get)

> data
[[1]]
  a
1 1
2 2
3 3

[[2]]
  a
1 4
2 5
3 6

R, assign content from .rda object with load()

2 Answers2