[R] matching using "which"

[R. Michael Weylandt]

Here's one that is perhaps a little simpler: simply drop the which and
use logical indexing.

dat <- matrix(1:6, 2); colnames(dat) <- c("A","B","A")

dat[, colnames(dat) %in% "A"]
dat[, colnames(dat) %in% "B"] # Note that you may want drop = FALSE
dat[, colnames(dat) %in% "C"]

dat[, !(colnames(dat) %in% "A")] # Note that you may want drop = FALSE
dat[, !(colnames(dat) %in% "B")]
dat[, !(colnames(dat) %in% "C")]

Michael


On Thu, Dec 8, 2011 at 7:42 AM, andrija djurovic <djandrija at gmail.com> wrote:
> Hi. Here is one approach:
>
> if (length(b)>0) data[,-b] else data
>
> Andrija
>
> On Thu, Dec 8, 2011 at 1:25 PM, Vikram Bahure <economics.vikram at gmail.com>wrote:
>
>> Dear R users,
>>
>> I have a very simple query.
>>
>> I am using the following command, which should give me row no. for the
>> matching colnames. It works well for matching the colnames but if there is
>> no column matching it gives me outcome as integer(0) which I am not able to
>> use in further calculation. It would be very helpful to have some insight.
>> *
>> *
>> *> b <- which(colnames(data)%in%c("X.","X"))*
>> *> b*
>> *integer(0)*
>> *> b>0*
>> *logical(0)*
>> *>b<- data[,-b]  # does not work properly*
>> *
>> *
>> Regards
>> Vikram
>>
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>>
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>
> ______________________________________________
> 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.