How can I load an object into a variable name that I specify from an R data file?

Question

When you save a variable in an R data file using save, it is saved under whatever name it had in the session that saved it. When I later go to load it from another session, it is loaded with the same name, which the loading script cannot possibly know. This name could overwrite an existing variable of the same name in the loading session. Is there a way to safely load an object from a data file into a specified variable name without risk of clobbering existing variables?

Example:

Saving session:

x = 5
save(x, file="x.Rda")

Loading session:

x = 7
load("x.Rda")
print(x) # This will print 5. Oops.

How I want it to work:

x = 7
y = load_object_from_file("x.Rda")
print(x) # should print 7
print(y) # should print 5

hadley · Accepted Answer · 2011-04-20T14:00:26.673

98

If you're just saving a single object, don't use an .Rdata file, use an .RDS file:

x <- 5
saveRDS(x, "x.rds")
y <- readRDS("x.rds")
all.equal(x, y)

edited Apr 20 '11 at 14:00

answered Apr 07 '11 at 13:40

hadley

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Updated to reflect that in 2.13 these are no longer experimental. – hadley Apr 20 '11 at 14:00
Does that mean that they're fully supported, just like .Rdata files? – Ryan C. Thompson Apr 23 '11 at 02:43
Since these are no longer experimental, I'm marking this as the accepted answer. This is what I've been using. – Ryan C. Thompson May 26 '12 at 19:56
Do `saveRDS` and `readRDS`, correspondingly, save and restore all object's attributes, including ones created by an application (via `attr`)? I tried to use this approach instead of `save` and `load`, trying to find a workaround for my problem. Howver, it doesn't seem to be the case, unless I'm doing something wrong: http://stackoverflow.com/questions/23701195/can-i-access-r-data-objects-attributes-without-fully-loading-objects-from-file. – Aleksandr Blekh May 18 '14 at 11:34

score 40 · Answer 2 · answered Aug 22 '14 at 21:44

40

I use the following:

loadRData <- function(fileName){
#loads an RData file, and returns it
    load(fileName)
    get(ls()[ls() != "fileName"])
}
d <- loadRData("~/blah/ricardo.RData")

answered Aug 22 '14 at 21:44

ricardo

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1

This is a great little function. Was having issues with trying to load things in (didnt want to just put them in the global environment as I know that was going to problems. – Trevor Nederlof Jun 04 '15 at 16:05
4

Something like this belongs in base R – Repmat Apr 10 '16 at 14:48
1

OMG. This is awesome. Just what I need! #loveit – Sander W. van der Laan Apr 14 '17 at 15:05
Can you please expand on the logic of the GET statement? Why not match to FILENAME instead of excluding? – nnachefski Dec 21 '17 at 18:01

score 37 · Answer 3 · answered Apr 07 '11 at 07:47

37

You can create a new environment, load the .rda file into that environment, and retrieve the object from there. However, this does impose some restrictions: either you know what the original name for your object is, or there is only one object saved in the file.

This function returns an object loaded from a supplied .rda file. If there is more than one object in the file, an arbitrary one is returned.

load_obj <- function(f)
{
    env <- new.env()
    nm <- load(f, env)[1]
    env[[nm]]
}

answered Apr 07 '11 at 07:47

Hong Ooi

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162

3

Is the `new.env` really necessary? Doesn't the function call itself provide a temporary environment? – Ryan C. Thompson Apr 07 '11 at 07:51
You can return whole environment (return(env) or return(environment()) when you modify function according to @Ryan suggestion). – Wojciech Sobala Apr 07 '11 at 12:55
2

If you use the function environment it will contain f and have a parent. Probably not what you want – hadley Apr 23 '11 at 13:51

score 28 · Answer 4 · answered Sep 17 '13 at 16:13

28

You could also try something like:

# Load the data, and store the name of the loaded object in x
x = load('data.Rsave')
# Get the object by its name
y = get(x)
# Remove the old object since you've stored it in y 
rm(x)

answered Sep 17 '13 at 16:13

by0

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5

The point is to avoid clobbering the value of x when loading. – Ryan C. Thompson Sep 17 '13 at 22:02

score 3 · Answer 5 · answered Aug 16 '19 at 18:01

3

Rdata file with one object

assign('newname', get(load('~/oldname.Rdata')))

answered Aug 16 '19 at 18:01

Javier Acosta

41
1

2

Won't this load the object into the old name, and then also assign it to the new name as well? That won't help if I'm worried about the possibility of overwriting an existing variable. – Ryan C. Thompson Aug 16 '19 at 18:11

score 2 · Answer 6 · answered Sep 28 '16 at 16:33

In case anyone is looking to do this with a plain source file, rather than a saved Rdata/RDS/Rda file, the solution is very similar to the one provided by @Hong Ooi

load_obj <- function(fileName) {

  local_env = new.env()
  source(file = fileName, local = local_env)

  return(local_env[[names(local_env)[1]]])

}

my_loaded_obj = load_obj(fileName = "TestSourceFile.R")

my_loaded_obj(7)

Prints:

[1] "Value of arg is 7"

And in the separate source file TestSourceFile.R

myTestFunction = function(arg) {
  print(paste0("Value of arg is ", arg))
}

Again, this solution only works if there is exactly one file, if there are more, then it will just return one of them (probably the first, but that is not guaranteed).

score 2 · Answer 7 · answered Jan 26 '21 at 15:06

Similar to the other solutions above, I load variables into an environment variable. This way if I load multiple variables from the .Rda, those will not clutter my environment.

load("x.Rda", dt <- new.env())

Demo:

x <- 2
y <- 1
save(x, y, file = "mydata.Rda")
rm(x, y)

x <- 123
# Load 'x' and 'y' into a new environment called 'dt'
load("mydata.Rda", dt <- new.env())
dt$x
#> [1] 2
x
#> [1] 123

score 1 · Answer 8 · answered Feb 15 '19 at 14:23

I'm extending the answer from @ricardo to allow selection of specific variable if the .Rdata file contains multiple variables (as my credits are low to edit an answer). It adds some lines to read user input after listing the variables contained in the .Rdata file.

loadRData <- function(fileName) {
  #loads an RData file, and returns it
  load(fileName)
  print(ls())
  n <- readline(prompt="Which variable to load? \n")
  get(ls()[as.integer(n)])
}

select_var <- loadRData('Multiple_variables.Rdata')

How can I load an object into a variable name that I specify from an R data file?

Example:

Saving session:

Loading session:

How I want it to work:

8 Answers8

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