[Rd] as.data.frame requires a lot of memory (PR#14140)

[rfalke at tzi.de]

Full_Name: Raimar Falke
Version: R version 2.10.0 (2009-10-26) 
OS: Linux 2.6.27-16-generic #1 SMP Tue Dec 1 19:26:23 UTC 2009 x86_64 GNU/Linux
Submission from: (NULL) (134.102.222.56)


The construction of a data frame in the way shown below requires
much more memory than expected. If we assume a cell value takes 8 bytes
the total amount of the data is 128mb. However the process takes about 
920mb and not the expected 256mb (two times the data set).

With the real data sets (~35000 observations with ~33000 attributes) the 
conversion to a data frame requires has to be killed at with 60gb of 
memory usage while it should only require 17.6gb (2*8.8gb).

  dfn <- rep(list(rep(0, 4096)), 4096)
  test <- as.data.frame.list(dfn)

I also tried the incremental construction of the 
data-frame: df$colN <- dataForColN. While I currently can't say much 
about the memory usage, it takes a looong time.

After the construction the saved-and-loaded data-frame has the expected size.

What is the recommended way to construct larger data-frames?