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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