R help - Jan 2008 - subsetting a data frame using string matching

Example data frame: 


a = c("Alpha", "Beta", "Gamma", "Beeta",
"Alpha", "beta")
b = c(1:6)
example = data.frame("Title" = a, "Vals" = b)

> example
  Title Vals
1 Alpha    1
2  Beta    2
3 Gamma    3
4 Beeta    4
5 Alpha    5
6  beta    6
> 
I would like to be able to get a new data frame from this data frame
containing only rows that match a certain string. In this case it
could for instance be the string "eta". I have tried various ways of
using agrep and grep, but so far I have not found anything that
worked.

Thankyou in advance for your help!

Karin
-- 
Karin Lagesen, PhD student
karin.lagesen at medisin.uio.no
http://folk.uio.no/karinlag

On 1/21/2008 5:18 AM, Karin Lagesen wrote:
> Example data frame: 
> 
> 
> a = c("Alpha", "Beta", "Gamma",
"Beeta", "Alpha", "beta")
> b = c(1:6)
> example = data.frame("Title" = a, "Vals" = b)
> 
> 
>> example
>   Title Vals
> 1 Alpha    1
> 2  Beta    2
> 3 Gamma    3
> 4 Beeta    4
> 5 Alpha    5
> 6  beta    6
> 
> I would like to be able to get a new data frame from this data frame
> containing only rows that match a certain string. In this case it
> could for instance be the string "eta". I have tried various ways
of
> using agrep and grep, but so far I have not found anything that
> worked.
> 
> Thankyou in advance for your help!
a <- c("Alpha", "Beta", "Gamma",
"Beeta", "Alpha", "beta")
b <- c(1:6)
df <- data.frame(Title = a, Vals = b)
df[grep("eta", df$Title),]
   Title Vals
2  Beta    2
4 Beeta    4
6  beta    6
> Karin
-- 
Chuck Cleland, Ph.D.
NDRI, Inc.
71 West 23rd Street, 8th floor
New York, NY 10010
tel: (212) 845-4495 (Tu, Th)
tel: (732) 512-0171 (M, W, F)
fax: (917) 438-0894

> a = c("Alpha", "Beta", "Gamma",
"Beeta", "Alpha", "beta")
> b = c(1:6)
> example = data.frame("Title" = a, "Vals" = b)
> 
> 
> > example
>   Title Vals
> 1 Alpha    1
> 2  Beta    2
> 3 Gamma    3
> 4 Beeta    4
> 5 Alpha    5
> 6  beta    6
> > 
> 
> I would like to be able to get a new data frame from this data frame
> containing only rows that match a certain string. In this case it
> could for instance be the string "eta". I have tried various ways
of
> using agrep and grep, but so far I have not found anything that
> worked.
Sounds like you were nearly there.

rows.to.keep <- grep("eta", example$Title)
subdata <- example[rows.to.keep,]

Regards,
Richie.

Mathematical Sciences Unit
HSL

"Statistics are like a lamp-post to a drunken man - more for leaning on 
than illumination."
David Brent, The Office.


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