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

[Moshe Olshansky]

Won't it be simpler to do:

for (i in 1:12){
data <- my.fun(my.list[i]))   
save(data,file = paste("data",i,".RData", sep="")) }


--- 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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