[BioC] How to create nested data frames

[Oleg Sklyar]

AFAIK it should be impossible, at least directly: a data.frame is
essentially a list of vectors of equal length. However, a matrix in R is
essentially a vector with dim attributes set. So what you can do is
something like this:

# function that uses such a crazy data.frame, x
f = function(x) {
  a = x$a
  dim(a) = attr(x,"matrixdim")
  b = x$b
  dim(b) = dim(a)
  # use matrices, e.g.
  print(dim(b))
}

m1 = matrix(runif(10),2,5)
m2 = matrix(runif(10),2,5)

df = data.frame(a=as.numeric(m1), b=as.numeric(m2))
attr(df, "matrixdim") = dim(m1)

f(df)

### should print 2 5 as those are the dimensions of matrices!
> f(df)
[1] 2 5

indeed!

Well, you need to consider that when you do as.numeric and when you do
'dim' on a vector - you copy the data! But honestly you can always find
a way to pass another object and a list would be more reasonable as you
do not need to copy data. And although the above example works I cannot
think of a situation where it would be justified to use it, also
data.frames are Slow!


-  
Dr Oleg Sklyar * EMBL-EBI, Cambridge CB10 1SD, UK * +441223494466


On Fri, 2007-10-26 at 00:19 +0200, Ana Conesa wrote:
> Dear List,
> 
> This is more an R than a Bioconductor question but I cannot post at
> the R list at the moment, so I apologize for using Bioconductor
> instead.
> 
> I am trying to use the pls package to compute pls regression of gene
> expression data on medical variables. I should provide my data as a
> data.frame (NOT A LIST) which contains the matrices of X and Y
> variables, i.e. if mydata is such data frame then mydata$expr gives
> the expression matrix and mydata$medical is the matrix of medical
> data. 
> If I do:
> >mydata <- data.frame(expr=expr, medical=medical)
> 
> I simply obtain a single data.frame combining the two and I am not
> able to call the matrices independently  I have been seaching the R
> help and documentation without sucess. 
> Any help appreciated.
> 
> Ana
> 
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