On Sep 18, 2011, at 11:10 AM, David Winsemius wrote:
On Sep 18, 2011, at 10:47 AM, Dennis Fisher wrote:
R 2.13.1
OS X
Colleagues
I frequently encounter a situation in which I want to remove a
single element of an array. For example, if I am reading in a
bunch of CSV files, I create the list of files to be read with:
LIST <- dir()
However, sometimes I want to exclude one or more files. I can
accomplish this with a second command:
LIST <- LIST[LIST != "filename.to.be.excluded"]
This is cumbersome -- is there some more efficient code to
accomplish this?
Doesn't negative indexing provide this?
?Extract
The most general way to convert character vectors to numbers for this
purpose is with grep which therefore supports regex patterns:
LIST <- dir(path="~/")
> length(LIST)
[1] 551
> LIST[1]
[1] "_train_1.dat"
> LIST <- LIST[ -grep("_train_1.dat", LIST) ]
> length(LIST)
[1] 550
Patterns can also be used in the dir() call.
--
David Winsemius, MD
West Hartford, CT
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