R help - Jun 2010 - Subset columns by prefix

Hello R listserve,

I would appreciate someone's help with this problem. Consider the following
toy dataset:

x <- read.table(textConnection("worldclim.1 worldclim.2 cru.1 cru.2
indv.1 7 8 32 658
indv.2 7 7 39 422"), header = TRUE)

How could I create a subset of the data based on the column prefix? For
instance, let's say I wanted to subset only the columns with the
"cru" prefix. Keep in mind that my real data set is very large and
likely to change through time, so simply subseting by column index -- e.g., x2
<- subset(x[,3:4]) -- would not be a good strategy.

Specific code that will give me the answer would be most valuable. I tried
looking up ?rm and ?ls, but I was not able to understand the syntax.

Thanks very much for your help!
Josh



      
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Try this:

subset(x, select = grep("cru", names(x)))

On Wed, Jun 9, 2010 at 2:41 PM, Josh B <joshb41@yahoo.com> wrote:
> Hello R listserve,
>
> I would appreciate someone's help with this problem. Consider the
following
> toy dataset:
>
> x <- read.table(textConnection("worldclim.1 worldclim.2 cru.1 cru.2
> indv.1 7 8 32 658
> indv.2 7 7 39 422"), header = TRUE)
>
> How could I create a subset of the data based on the column prefix? For
> instance, let's say I wanted to subset only the columns with the
"cru"
> prefix. Keep in mind that my real data set is very large and likely to
> change through time, so simply subseting by column index -- e.g., x2 <-
> subset(x[,3:4]) -- would not be a good strategy.
>
> Specific code that will give me the answer would be most valuable. I tried
> looking up ?rm and ?ls, but I was not able to understand the syntax.
>
> Thanks very much for your help!
> Josh
>
>
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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