[R] [r] regression coefficient for different factors

[Dimitri Liakhovitski]

Francesco, do you just want a separate regression for each level of
your factor c?
You could write a loop - looping through levels of c:

for(i in levels(c)){
   select your data here and write a regression formula
}

On Fri, May 20, 2011 at 9:39 AM, Francesco Nutini
<nutini.francesco at gmail.com> wrote:
>
> Thanks for your reply,
>
> ?summary produce a  multiple r2.
> My dataset il similar to this one:
>
>>            a         b   c
>> 1 -1.4805676 0.9729927 x
>> 2  1.5771695 0.2172974 x
>> 3 -0.9567445 0.5205087 x
>> 4 -0.9200052 0.8279428 z
>> 5 -1.9976421 0.9641110 z
>> 6 -0.2722960 0.6318801 y
>
> So, I would like to know the r2 for a~b for every factors levels.
> Off course I can made the regression separately for every factors, but my dataset have 68 factors...
>
> ----------
> Francesco Nutini
> PhD student
> CNR-IREA (Institute for Electromagnetic Sensing of the Environment)
> Milano, Italy
>
>  > From: rbaer at atsu.edu
>> To: nutini.francesco at gmail.com; r-help at r-project.org
>> Subject: Re: [R] [r] regression coefficient for different factors
>> Date: Fri, 20 May 2011 08:07:59 -0500
>>
>> ?summary
>>
>> produces r^2 in 2nd to last line, as in,
>> > set.seed(12); a=rnorm(100); b = runif(100); c = factor(rep(c('No',
>> > 'Yes'),50)); df = data.frame(a,b,c)
>> > head(df)
>>            a         b   c
>> 1 -1.4805676 0.9729927  No
>> 2  1.5771695 0.2172974 Yes
>> 3 -0.9567445 0.5205087  No
>> 4 -0.9200052 0.8279428 Yes
>> 5 -1.9976421 0.9641110  No
>> 6 -0.2722960 0.6318801 Yes
>> > mod = lm(a ~ b*c)
>> > summary(mod)
>>
>> Call:
>> lm(formula = a ~ b * c)
>>
>> Residuals:
>>     Min      1Q  Median      3Q     Max
>> -1.8196 -0.4754 -0.0246  0.5585  2.0941
>>
>> Coefficients:
>>             Estimate Std. Error t value Pr(>|t|)
>> (Intercept)   0.2293     0.2314   0.991    0.324
>> b            -0.4226     0.3885  -1.088    0.280
>> cYes          0.1578     0.3202   0.493    0.623
>> b:cYes       -0.5878     0.5621  -1.046    0.298
>>
>> Residual standard error: 0.8455 on 96 degrees of freedom
>> Multiple R-squared: 0.07385,  Adjusted R-squared: 0.04491
>> F-statistic: 2.552 on 3 and 96 DF,  p-value: 0.0601
>>
>> ------------------------------------------
>> Robert W. Baer, Ph.D.
>> Professor of Physiology
>> Kirksville College of Osteopathic Medicine
>> A. T. Still University of Health Sciences
>> 800 W. Jefferson St.
>> Kirksville, MO 63501
>> 660-626-2322
>> FAX 660-626-2965
>>
>>
>> --------------------------------------------------
>> From: "Francesco Nutini" <nutini.francesco at gmail.com>
>> Sent: Friday, May 20, 2011 4:17 AM
>> To: "[R] help" <r-help at r-project.org>
>> Subject: [R] [r] regression coefficient for different factors
>>
>> >
>> > Dear R-helpers,
>> >
>> > In my dataset I have two continuous variable (A and B) and one factor.
>> > I'm investigating the regression between the two variables usign the
>> > command
>> > lm(A ~ B, ...)
>> > but now I want to know the regression coefficient (r2) of A vs. B for
>> > every factors.
>> > I know that I can obtain this information with excel, but the factor have
>> > 68 levels...maybe [r] have a useful command.
>> >
>> > Thanks,
>> >
>> > Francesco Nutini
>> >
>> > [[alternative HTML version deleted]]
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > 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.
>> >
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>



-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com