[R] Reading multiple files into R

[Kevin Bartz]

Roger Bivand wrote:
> 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
>>
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>>
> 
> 

Good call. Here's a somewhat more R-ified version:

res <- lapply(paste("wb-", formatC(1:99, width=2, flag="0"), "vc.dbf",
                     sep=""), maptools:::dbf.read)

Kevin