[R] linear regression, exclude a datum

[e-letter]

On 15/09/2009, Uwe Ligges <ligges at statistik.tu-dortmund.de> wrote:
>
>
> e-letter wrote:
>> On 14/09/2009, Steve Lianoglou <mailinglist.honeypot at gmail.com> wrote:
>>> Hi,
>>>
>>> On Sep 14, 2009, at 9:47 AM, e-letter wrote:
>>>
>>>> Readers,
>>>>
>>>> I have been reading the r book (Crawley) and tried to use the
>>>> influence measures function for linear regression, as described. I
>>>> have one datum that I wish to show in the graph but exclude from the
>>>> regression and ab line.
>>>>
>>>> x	y
>>>> 0	5
>>>> 10	9
>>>> 20	10
>>>> 30	19
>>>> 40	4
>>>>
>>>> With the influence measures function I plot the graph but linear
>>>> regression includes the datum (40,4), which I want to show on the
>>>> graph but exclude from the linear regression ab line.
>>>>
>>>> Is there an alternative package to perform this task please?
>>> Please post the code you're using to try and do the regression.
>>>
>>> I think you simply want to remove the data point when you build the
>>> regression model, then plot it later after you plot the regression.
>>>
>> Correct; below are my commands:
>>
>>  x<-c(0,10,20,30)
>>  y<-c(5,9,12,19)
>>  fit<-lm(y~x)
>>  plot(y~x)
>>  abline(fit)
>>
>> I try these commands as explained in section 12 (graphics) of the
>> introduction manual:
>
>
>
> Hope this example is not in Crawley's book as you cite it, because you
> need to make the plot large enough to include the value (40,4) already
> when you create the plot, e.g., by specifying xlim and ylim.
>
No, it is an example I made quickly to post to the mailing list. Which
section of the manual explains xlim please?

> Anyway, I'd rather explude the value from a data.frame as fol#ows:
>
> # whole data:
> dat <- data.frame(x = c(0,10,20,30,40), y = c(5,9,12,19,4))
> dat
> plot(y~x, data=dat)
> # fit the regression without the 5th observation:
> fit <- lm(y ~ x, data=dat[-5,])
> abline(fit)
>
Thank you. Please advise which section of the introduction manual
explains how to exclude a datum (the instruction '...dat[-5,]'. One of
my biggest difficulties is finding the relevant section of the
manual(s).