[R] Reading data into R

[Gabor Grothendieck]

On Jan 3, 2008 9:00 AM, BEP <perronbe at gmail.com> wrote:
> Hello all,
>
> I am working with a very large data set into R, and I have no interest in
> reviving my SAS skills.  To do this, I will need to drop unwanted variables
> given the size of the data file.  The most common strategy seems to be
> subsetting the data after it is read into R.  Unfortunately, given the size
> of the data set, I can't get the file read and then subsquently do the
> subset procedure.  I would be appreciative of help on the following:
>
> 1.  What are the possibilities of reading in just a small set of variables
> during the <read.table> statement (or another 'read' statement)?  That is,
> is it possible specify just the variables that I want to keep?

read.table can skip columns.  Specify the releveant component of colClasses
as NULL.

>
> 2.  Can I randomly select a set of observations during the 'read' statement?
>
>
> I have searched various R resources for this information, so if I am simply
> overlooking a key resource on this issue, pointing that out to me would be
> greatly appreciated.
>

The development version of sqldf can do all of the above (i.e. read in
a subset of
columns, a subset of rows or a random subset of rows) subject to certain
limitations on the input format.  See Example 6 on the home page:
   http://sqldf.googlecode.com

readTable in the R.utils package can also read in a subset of rows and columns.