[R] automatically generating and accessing data frames of varying dimensions

[Gabor Grothendieck]

Its desirable to put the data frames into a list so they can be easily
iterated over in the future.  Try this:

auto.length <- 2:4 # replace with desired row lengths
f <- function(names, nr) {
	x <- rep(0, nr)
	data.frame(X1 = x, X2 = x, X3 = x)
}
auto.names <- paste("auto.data", seq_along(auto.length), sep = ".")
mapply(f, auto.names, auto.length, SIMPLIFY = FALSE)


On 7/12/07, Drescher, Michael (MNR) <michael.drescher at ontario.ca> wrote:
> Hi All,
>
> I want to automatically generate a number of data frames, each with an
> automatically generated name and an automatically generated number of
> rows. The number of rows has been calculated before and is different for
> all data frames (e.g. c(4,5,2)). The number of columns is known a priori
> and the same for all data frames (e.g. c(3,3,3)). The resulting data
> frames could look something like this:
>
> > auto.data.1
>  X1 X2 X3
> 1  0  0  0
> 2  0  0  0
> 3  0  0  0
> 4  0  0  0
>
> > auto.data.2
>  X1 X2 X3
> 1  0  0  0
> 2  0  0  0
> 3  0  0  0
> 4  0  0  0
> 5  0  0  0
>
> > auto.data.3
>  X1 X2 X3
> 1  0  0  0
> 2  0  0  0
>
> Later, I want to fill the elements of the data frames with values read
> from somewhere else, automatically looping through the previously
> generated data frames.
>
> I know that I can automatically generate variables with the right number
> of elements with something like this:
>
> > auto.length <- c(12,15,6)
> > for(i in 1:3) {
> + nam <- paste("auto.data",i, sep=".")
> + assign(nam, 1:auto.length[i])
> + }
> > auto.data.1
>  [1]  1  2  3  4  5  6  7  8  9 10 11 12
> > auto.data.2
>  [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
> > auto.data.3
> [1]  1 2 3 4 5 6
>
> But how do I turn these variables into data frames or give them any
> dimensions? Any commands such as 'as.matrix', 'data.frame', or 'dim' do
> not seem to work. I also seem not to be able to access the variables
> with something like "auto.data.i" since:
>
> > auto.data.i
> Error: object "auto.data.i" not found
>
> Thus, how would I be able to automatically write to the elements of the
> data frames later in a loop such as ...
>
> > for(i in 1:3) {
> + for(j in 1:nrow(auto.data.i)) {       ### this obviously does not work
> since 'Error in nrow(auto.data.i) : object "auto.data.i" not found'
> + for(k in 1:ncol(auto.data.i)) {
> + auto.data.i[j,k] <- 'some value'
> + }}}
>
> Thanks a bunch for all your help.
>
> Best, Michael
>
>
> Michael Drescher
> Ontario Forest Research Institute
> Ontario Ministry of Natural Resources
> 1235 Queen St East
> Sault Ste Marie, ON, P6A 2E3
> Tel: (705) 946-7406
> Fax: (705) 946-2030
>
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