[R] subsetting a dataframe

[Chuck Cleland]

On 3/4/2008 8:41 AM, John Sorkin wrote:
> windows XP
> R 2.6.0
> 
> I am having problems deleting a row from a data frame. I create my dataframe by subsetting a larger dataframe:
> 
> ShortLavin<-Lavin[Lavin[,"Site"]=="PP" | Lavin[,"Site"]=="CC" | Lavin[,"Site"]=="FH",]

   I would do that in the following way:

ShortLavin <- subset(Lavin, Site %in% c("PP","CC","FH"))

> I then perform a glm using the data frame and plot the results. 
> 
> fit1poisson<-glm(NumUniqOpPt~Seq+Site,family=poisson(link = "log"),data=ShortLavin,offset=log(NumUniqPt))
> plot(fit1poisson)

   Of course, you could have done the subsetting within the call to glm:

fit1poisson <- glm(NumUniqOpPt~Seq+Site,family=poisson(link = "log"),
data=subset(Lavin, Site %in% c("PP","CC","FH")),
offset=log(NumUniqPt))

> On the plots I see a point labeled as 127 that is an extreme value. I want to re-run the glm excluding the extreme observation. I have tried several methods to exclude the observation (shown below), none have worked. 
> 
> Minus127<-ShortLavin[-127,]
> Minus127<-ShortLavin[-"127",]
> Minus127<-ShortLavin[-c(127),]
> Minus127<-ShortLavin[-c("127"),]
> 
> None of these worked. Suggestions on how I can remove observation 127 would be appreciated

Minus127 <- subset(ShortLavin, !rownames(ShortLavin) %in% 127)

> Thank you,
> John
> 
> John Sorkin M.D., Ph.D.
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
> 
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-- 
Chuck Cleland, Ph.D.
NDRI, Inc.
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