How can I load an object into a variable name that

问题:

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

回答1:

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)

回答2:

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]]
}

回答3:

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")

回答4:

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)

回答5:

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).

回答6:

Rdata file with one object

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

回答7:

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')