R help - Aug 2001 - Processing all *.dat worked. Thanks

I got great, quick advice here earlier today.  One little hitch was that
the pattern in list.files wants a regular expression, and *.dat was
grabbing all files with .dat in them, not ones ending in .dat.  This
code creates a *.dat.summary file with the mean and std. deviation. of
the numeric variables for every *.dat file in the current directory.

myDat<-list.files(pattern="*.dat$")
createSummary <-function(dsName){
  data<-read.table(dsName,header=T,as.is = TRUE)
  indices<-1:dim(data)[2]
  indices<-na.omit(ifelse(indices*sapply(data,is.numeric),indices,NA))
  mean<-sapply(data[,indices],mean)
  sd<-sapply(data[,indices],sd)
  newOutput<-rbind(mean,sd)
  newOutput<-round(newOutput,digits=6)
  outputdsname<-c(paste(dsName,".summary",sep=""))
  write.table(t(newOutput),file=outputdsname,quote=FALSE,
sep="\t",col.names=FALSE)
}

processData <-function(dat){
  for (i in 1:length(dat))
  {
    createSummary(dat[[i]])
  }
}

processData(myDat)


-- 
Paul E. Johnson                       email: pauljohn at ukans.edu
Dept. of Political Science            http://lark.cc.ukans.edu/~pauljohn
University of Kansas                  Office: (785) 864-9086
Lawrence, Kansas 66045                FAX: (785) 864-5700
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>>>>> "PaulEJ" == Paul E Johnson <pauljohn at
ukans.edu> writes:
    PaulEJ> I got great, quick advice here earlier today.  One little hitch
    PaulEJ> was that the pattern in list.files wants a regular expression,
    PaulEJ> and *.dat was grabbing all files with .dat in them, not ones
    PaulEJ> ending in .dat.  This code creates a *.dat.summary file with
    PaulEJ> the mean and std. deviation. of the numeric variables for every
    PaulEJ> *.dat file in the current directory.

    PaulEJ> myDat<-list.files(pattern="*.dat$")

(many of us would say  ``please use spaces around "<-" ''
 [recent versions of ESS do this automagically with the "_" key!])

    PaulEJ>  <.....>

You are right: Pattern should be a  *regular expression*

However, it was ``pure luck'' that your  "*.dat$"  worked
fine.
Both "*" and "." don't mean what you think they mean;

  "."  means  ``any arbitrary character''
  "*"  means  ``the previous [thing] arbitrary many (0,1,...)
times''
	      where [thing] is a single character (or something more general
						   for advanced usage)

The correct pattern would have been

    pattern = "\\.dat$"

which really is \.dat$ 
{ the "\\" (doubling) is necessary to specify a single "\"
in an R string}

You can find a bit more about regular expression using R's help
  ?grep    and
  ?apropos

Regular Expressions (nicknamed "Regexp"s, "Regex"s or
"RE"s) are a very
powerful concept from the early years of Unix; probably first used for the
"grep" (and "egrep") command; then, inside Emacs and lately
Perl, Python,
etc.  All regexp implementations have quite a few things in common,
but slightly differ when it becomes complicated.  
It's worth spending an hour or so learning the basics.
A google search gives you tons of starting points.


Martin Maechler <maechler at stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><
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r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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