[R] importing many csv files into separate matrices

[Henrik Bengtsson]

On Wed, Dec 4, 2013 at 6:53 PM, Greg Snow <538280 at gmail.com> wrote:
> As you have noticed, using assign is not simple, and your approach has
> potential to cause even more problems even if you get it working.
> Here is another approach:
>
> loadCSVfiles <- function(path) {
>   x <- list.files(path, full.names=TRUE)
>   out <- lapply( x, read.csv )
>   names(out) <- sub(pattern="\\.csv$", replacement="", x)
>   out
> }
>
> then run:
>
> mydata <- loadCSVfiles("/my/path")

I fully agree with this; instead of messing around with assign() -
ending up using assign() is often a good indicator that there is
another better way to do it.

BTW, read.csv() returns a data.frame (not a matrix) just as read.table() do.

An alternative to the above loadCSVfiles() function, is to use the
R.filesets package, e.g.

library("R.filesets")
ds <- TabularTextFileSet$byPath("/my/path", pattern="[.]csv$")
mydata <- lapply(ds, FUN=readDataFrame)

That also sets the names by the filenames w/out the extension.  If one
don't like that style, the same thing can be achieved by:

library("R.filesets")
files <- dir(path="/my/path", pattern="[.]csv$", full.names=TRUE)
mydata <- readDataFrame(files, combineBy=NULL)

/Henrik

>
> and mydata will be a list with all of your data objects with the
> desired names.  You can do things like:
>
> plot(mydata$alaska)
>
> or
>
> with(mydata, plot(alaska))
>
> or
>
> lapply( mydata, plot )
>
> etc.
>
> This approach does not place the individual objects into the global
> workspace, but that is a good thing.
>
> On Wed, Nov 27, 2013 at 3:39 PM, yetik serbest <yserbest at prodigy.net> wrote:
>> Hi Everyone,
>>
>> I am trying to import many CSV files to their own matrices. Example, alaska_93.csv to alaska. When I execute the following, for each csv.file separately it is successful.
>>
>> singleCSVFile2Matrix <- function(x,path) {
>>  assign(gsub(pattern=".csv",x,replacement=""),read.csv(paste(path,x,sep="")))
>> }
>>
>> when I try to include it in a loop in another function (I have so many csv files to import), it doesn't work. I mean the following function doesn't do it.
>>
>> loadCSVFiles_old <- function(path) {
>>  x <- list.files(path)
>>  for (i in 1:length(x)) {
>>   assign(gsub(pattern=".csv",x[i],replacement=""),read.csv(paste(path,x[i],sep="")))
>>   }
>> }
>>
>> Instead, if I execute the foor loop in the command line, it works. I am puzzled. Appreciate any help.
>>
>> thanks
>> yetik
>>
>> ______________________________________________
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> 538280 at gmail.com
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.