[R] Reading multiple files into R

[Vikas Rawal]

Thanks Kevin and Roger. This gave me the clue and was a great help.
I have been trying it out. There is some problem in the code that still 
needs to be figured out.

For the first 9 files, paste("wb-0", i, "vc.dbf", sep="") works fine.
But as you rightly guessed, I have more files.
So when I use paste("wb-", formatC(i, width=2, flag="0"), "vc.dbf", 
sep=""), dbf.read does not work.
formatC works find if I use it in cat(paste.................). It 
displays the file names correctly.
But when I use it in dbf.read, it gives the following error.

***********************
res[[i]] <- maptools:::dbf.read(paste("wb-", format(i, width=2,flag=0), 
"vc.dbf", sep=""))
Error in maptools:::dbf.read(paste("wb-", format(i, width=2,flag=0), 
"vc.dbf", sep=""))
Error in maptools:::dbf.read(paste("wb-", format(i, width = 2, flag = 
0),  :
    unable to open DBF file
***********************

Of course, the data files are all right. I can read them individually.

What do you think could be the problem?

Vikas

Kevin Bartz wrote:

> 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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>>> PLEASE do read the posting guide! 
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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
>
>
>