On Aug 22, 2011, at 1:45 PM, Dennis Murphy wrote:
Hi:
You need a leading ^ in your grep string. Here's a reproducible
example to illustrate:
df <- data.frame(Xyz1 = rnorm(5), Xyz2 = rnorm(5), Xyz3 = rnorm(5),
Abc1 = rnorm(5), Abc2 = rnorm(5))
df[, grep('^Xyz', names(df))]
df[, grep('^Abc', names(df))]
The leading "^" should not be necessary to solve the problem of "no
matches at all" reported in the followup message, since it narrows the
search rather than expanding it. It would only be necessary if there
were column names that you wanted to exlcude where "Xyz" was not at
the beginning of the string. My guess is that th eOP does not realize
the importantce of capitaliszation and that all these are different so
would NOT be matched by grep("Xyz" ,...): "xyz", xYz", "xyZ".
HTH,
Dennis
On Mon, Aug 22, 2011 at 7:33 AM, Jay <josip.2...@gmail.com> wrote:
Hi,
Let's say that I have a set of column names that begin with the
string
"Xyz". How do I extract these specific columns? I tried to do the
following:
dataframe1[,grep("Xyz",colnames(dataframe1))]
But it does not work. What is wrong with my expression?
--
David Winsemius, MD
West Hartford, CT
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