[R] Reading multiple files into R

[Roger Bivand]

On Fri, 1 Oct 2004, Vikas Rawal wrote:

> I want to read data from a number of files into R.
> Reading individual files one by one requires writing enormous amount of 
> code that will look something like the following.
> 
> ****************
> maptools:::dbf.read("wb-01vc.dbf")->dist1
> maptools:::dbf.read("wb-02vc.dbf")->dist2
> maptools:::dbf.read("wb-03vc.dbf")->dist3
> maptools:::dbf.read("wb-04vc.dbf")->dist4
> maptools:::dbf.read("wb-05vc.dbf")->dist5
> maptools:::dbf.read("wb-06vc.dbf")->dist6
> maptools:::dbf.read("wb-07vc.dbf")->dist7
> maptools:::dbf.read("wb-08vc.dbf")->dist8
> maptools:::dbf.read("wb-09vc.dbf")->dist9
> *****************
> 

In this case, you could pre-allocate a list and:

res <- vector(mode="list", length=9)
for (i in 1:length(res)) 
    res[[i]] <- maptools:::dbf.read(paste("wb-0", i, "vc.dbf", sep=""))

> res <- vector(mode="list", length=9)
> for (i in 1:length(res)) cat(paste("wb-0", i, "vc.dbf", sep=""), "\n")
wb-01vc.dbf 
wb-02vc.dbf 
wb-03vc.dbf 
...

gives a check on what file names are being used.

For 10 to 99 preserving the 01-09, use paste("wb-", formatC(i, width=2, 
flag="0"), "vc.dbf", sep="").

If the token is a character (string) that varies, you can roll out a 
character vector of tokens first and step along it.

> res <- vector(mode="list", length=length(LETTERS))
> for (i in 1:length(res)) cat(paste("wb-", LETTERS[i], "vc.dbf", sep=""), 
+ "\n")
wb-Avc.dbf 
wb-Bvc.dbf 
wb-Cvc.dbf 
...


> Is there a better way of doing this?
> 
> Vikas
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no