That works! Thanks.
On Mon, Aug 15, 2011 at 5:09 PM, Bert Gunter <gunter.ber...@gene.com> wrote:
> Sverre:
>
> As your reproducible example shows, the problem is that the string
> "y1:y2" is not an acceptable term of the formula. One way round this
> is simply convert the non-string part of the formula to a string, pase
> it with your term, and then reconvert it to a formula:
>
> update(my.lm,formula(paste(".~.-", my.object)))
>
> There may be a more elegant way via substitute(), but I think this works.
>
> Cheers,
> Bert
>
> On Mon, Aug 15, 2011 at 1:44 PM, Sverre Stausland
> <john...@fas.harvard.edu> wrote:
>> Hi all,
>>
>> I'm extracting the name of the term in a regression model that
>> dropterm specifies as the least significant one, and I'm assigning
>> this name to an object. However, when I use update(), it ignores this
>> object. Is there a way I can make it not ignore it? A reproducible
>> example is below:
>>
>>> lm(x1~1+y1*y2+y3+y4,data=anscombe)->my.lm
>>> rownames(dropterm(my.lm,test="F",sort=TRUE))[1]->my.object
>>> my.object
>> [1] "y1:y2"
>>> update(my.lm,.~.-my.object)
>>
>> Call:
>> lm(formula = x1 ~ y1 + y2 + y3 + y4 + y1:y2, data = anscombe)
>>
>> Coefficients:
>> (Intercept) y1 y2 y3 y4
>> -8.95635 1.11420 0.61921 0.76762 0.21237
>> y1:y2
>> -0.04056
>>
>>> update(my.lm,.~.-y1:y2)
>>
>> Call:
>> lm(formula = x1 ~ y1 + y2 + y3 + y4, data = anscombe)
>>
>> Coefficients:
>> (Intercept) y1 y2 y3 y4
>> -6.6409 0.7618 0.3836 0.7759 0.1640
>>
>> ______________________________________________
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>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
>
> --
> "Men by nature long to get on to the ultimate truths, and will often
> be impatient with elementary studies or fight shy of them. If it were
> possible to reach the ultimate truths without the elementary studies
> usually prefixed to them, these would not be preparatory studies but
> superfluous diversions."
>
> -- Maimonides (1135-1204)
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
>
>
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