[R] Relational Databases or XML?

[Gabor Grothendieck]

You may wish to try out sqldf.  It allows one to manipulate data
frames using sql.  The real work is
done by sqlite and the RSQLite interface but it sets up the database
for you and all the tables
and then deletes them so its as easy a typing in one line of code.
Check out the home page
at http://sqldf.googlecode.com .

On Windows sqlite is included in the RSQLite package so you have
nothing to install but
an ordinary R package.

For XML there is the XML R package.  The ctv and Ryacas packages are
two packages
that use XML (for the task view database and for parsing OpenMath
respectively).  At
least on Windows you just install the XML package and it includes
everything you need.
On omegahat site there is more about the R XML package.  There is also a package
to handle pubmed in XML in bioconductor.

On Thu, Apr 10, 2008 at 4:14 PM, Keith Alan Chamberlain
<Keith.Chamberlain at colorado.edu> wrote:
> Dear R-Help,
>
> I am working on a paper in an R course for large file support in R using scan(), relational databases, and XML. I have never used SQL or heirarchical document formats such as XML (except where it occurs without user interaction), and knowledge in RDBs and XML is lacking in my program. I have tried finding a working example for the novices-novice on the topic, read many postings, the r-data I/O manual several times, and descriptions of packages RODBC, DBI, XML, among others. I understand that RDBs are (assumed at least) used widely among the R community. I have not been able to put all of the pieces together, but assuming that RDB use is actually quite widespread, it should be quite easy to fill me in and/or correct my understanding where necessary.
>
> For a cross-platform solution (PC/OSX at least, or in part) my questions/problems are about what preliminary steps are needed to get an SQL or XML query "to work" in R to begin with, what the appropriate data-file formats are, and how to convert to them if starting out with data in, say, a delimited ASCII text file. Very basic examples should suffice, say, a table with 20 random observations, a grouping variable with 2 levels, and a factor with 2 levels.
>
> ## untested code
> set.seed(1024)
> write.table("junk.txt", data.frame(Subj=c(rep(1,10),rep(2,10)),block=rep(c(rep(-1,5),rep(1,5)),2), obs=rnorm(20,0,1)))
>
> Specifically,
>
> 1- what are the minimum required non R components that are needed to support SQL or XML functionality, which may or may not need to be installed?
>
> 2- what R packages need to be installed, at a minimum (also as a cross-PC/Mac solution if possible or at least as much as possible)
>
> 3- I keep seeing reference to connections of a given name "if previously setup". What kind of setup is needed outside of R, if any?
>
> 4- what steps are needed in R to then connect to a file and import a subset based on a query?
>
> 5- Do I then use standard R routines (e.g. write()) to export as a DB, or an RDB/XML specific function?
>
> Sincerely,
> KeithC. [U.S]
>
> 1/k^c
>
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