On Jan 30, 2012, at 2:30 AM, David Studer wrote:
Hello,
I have the following question:
when creating a data.frame
a1<-c(1,2,3)
a2<-c(1,2,3)
c<-data.frame(a1,a2)
I can select columns using an index like:
c[,1:2]
Is this possible too when using column-names? (something like
c(,"a1":"a2"),
which doesn't work):
Generally you need to use grep to convert column names to numbers for
use within "[" operations]
df[ , grep("^a1$", names(df)):grep"^"a2$", names(df)) ]
--
Another David
Alternative question: Is there a function to get the index of a
variable by
name
That's what grep will do.
or can I
select certain columns using a loop? (a_1, a_2, ..., a_n)
Thank you very much!
David
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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