[R] assigning and saving datasets in a loop, with names changing with "i"

[Henrik Bengtsson]

library(R.utils);

for (ii in 1:12) {
  value <- my.fun(my.list[ii]);
  saveObject(value, file=sprintf("data%02d.RData", ii));
  rm(value); gc();
}

for (ii in 1:12) {
  value <- loadObject(sprintf("data%02d.RData", ii));
}


On 18/12/2007, Marie Pierre Sylvestre <MP.Sylvestre at epimgh.mcgill.ca> wrote:
> Dear R users,
>
> I am analysing a very large data set and I need to perform several data
> manipulations. The dataset is so big that the only way I can play with it
> without having memory problems (E.g. "cannot allocate vectors of size...")
> is to write a batch script to:
>
> 1. cut the data into pieces
> 2. save the pieces in seperate .RData files
> 3. Remove everything from the environment
> 4. load one of the piece
> 5. perform the manipulations on it
> 6. save it and remove it from the environment
> 7. Redo 4-6 for every piece
> 8. Merge everything together at the end
>
> It works if coded line by line but since I'll have to perform these tasks
> on other data sets, I am trying to automate this as much as I can.
>
> I am using a loop in which I used 'assign' and 'get' (pseudo code below).
> My problem is when I use 'get', it prints the whole object on the screen.
> I am wondering whether there is a more efficient way to do what I need to
> do. Any help would be appreciated. Please keep in mind that the whole
> process is quite computer-intensive, so I can't keep everything in the
> environment while R performs calculations.
>
> Say I have 1 big dataframe called data. I use 'split' to divide it into a
> list of 12 dataframes (call this list my.list)
>
> my.fun is a function that takes a dataframe, performs several
> manipulations on it and returns a dataframe.
>
>
> for (i in 1:12){
>   assign( paste( "data", i, sep=""),  my.fun(my.list[i]))   # this works
>   # now I need to save this new object as a RData.
>
>   # The following line does not work
>   save(paste("data", i, sep = ""),  file = paste(  paste("data", i, sep =
> ""), "RData", sep="."))
> }
>
>   # This works but it is a bit convoluted!!!
>   temp <- get(paste("data", i, sep = ""))
>   save(temp,  file = "lala.RData")
> }
>
>
> I am *sure* there is something more clever to do but I can't find it. Any
> help would be appreciated.
>
> best regards,
>
> MP
>
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