R help - May 2012 - NA's when subset in a dataframe

Dear community, 

I'm having this silly problem.

I've a linear model. After fixing it, I wanted to know which data had
studentized residuals larger than 3, so i tried this: 

d1 <- cooks.distance(lmmodel)
r <- sqrt(abs(rstandard(lmmodel)))
rstu <- abs(rstudent(lmmodel))

a <- cbind( mydata, d1, r,rstu) 

alargerthan3 <-  a[rstu >3, ]

And suddenly  a[rstu >3, ]  has 17 rows, 7 of them are "new rows",
where all
the entries are NA's, even its rownames. 

Because of this I'm not sure of the dimension of    a[rstu >3, ]  (Do I
only
have 8 entries?)

Has this happened to anybody before? If so, why this extra NA rows? what's
the problem? Is there any other way to know which data have studentized
residuals larger than   3?


 if it's needed  to upload my data, just tell me.

Thanks in advance,show crosspide at hotmail.com as user at host.com




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Le jeudi 03 mai 2012 ? 07:37 -0700, agent dunham a ?crit
:
> Dear community, 
> 
> I'm having this silly problem.
> 
> I've a linear model. After fixing it, I wanted to know which data had
> studentized residuals larger than 3, so i tried this: 
> 
> d1 <- cooks.distance(lmmodel)
> r <- sqrt(abs(rstandard(lmmodel)))
> rstu <- abs(rstudent(lmmodel))
> 
> a <- cbind( mydata, d1, r,rstu) 
> 
> alargerthan3 <-  a[rstu >3, ]
> 
> And suddenly  a[rstu >3, ]  has 17 rows, 7 of them are "new
rows", where all
> the entries are NA's, even its rownames. 
> 
> Because of this I'm not sure of the dimension of    a[rstu >3, ] 
(Do I only
> have 8 entries?)
> 
> Has this happened to anybody before? If so, why this extra NA rows?
what's
> the problem? Is there any other way to know which data have studentized
> residuals larger than   3?
> 
> 
>  if it's needed  to upload my data, just tell me.
A small reproducible example would have been better. Anyway, see page 88
of The R Inferno.

In your case, the simplest solutions are to do:
alargerthan3 <- a[which(rstu > 3),]
or
alargerthan3 <- subset(a, rstu > 3)


Cheers