[R] how exactly does 'identify' work?

[Greg Snow]

Did you read the help page for qqnorm?  The return value has the x and y coordinates used, you can just do something like:

> tmp <- qqnorm( resid(test.lm) )
> identify(tmp, , names(resid(test.lm)) )

Or the plot.lm function has an argument id.n that automatically labels the n most extreme values:

> plot( test.lm, 2, id.n=10 )

Those both worked in my tests, if they are not working for you then send a reproducible example (include data, see ?dput) and maybe we can help further.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of casperyc
> Sent: Thursday, November 18, 2010 11:50 AM
> To: r-help at r-project.org
> Subject: Re: [R] how exactly does 'identify' work?
> 
> 
> Hi,
> 
> I think the problem is
> 
> 1 - when a linear model is fitted, ploting the qqnorm( test.lm$ res )
> we dont 'know' what values are actually being used on the y-axis; and
> how do we refer to the ‘Index’ on the x-axis??
>      therefore, i dont know how to refer to the x and y coordinates in
> the
> identify function
> 
> 2 - i have tried using the stdres function in the MASS library, to
> extract
> the standardised
> residuals and plot them manully, ( using the plot ) function.
>      this way, the problem is we have to SORT the residuals first in
> increasing order to reproduce the same qqnorm plot, in that case,
> 'identify'
> function works, however, that CHANGES the order, i.e. it wont return
> the
> original A:Z ( row.names ) label.
> --
> View this message in context: http://r.789695.n4.nabble.com/how-
> exactly-does-identify-work-tp3045953p3049357.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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