regression coefficient for different factors

Please forgive me for all these questions Dimitri...

I'm running these input:

mylist<-NULL #in order to hold my input
for(i in levels(mydataset$c)) { temp.data<-mydataset [mydataset$c %in 
% i]

mylist[[i]]<- lm(temp.data$a ~ temp.data$b , data=temp.data) }


That's the erros returns
Error in `[.data.frame`(mydataset, niger$site %in% i) :
"undefined columns selected"

Date: Fri, 20 May 2011 10:01:39 -0400
Subject: Re: [R] [r] regression coefficient for different factors
From: dimitri.liakhovitski at gmail.com
To: nutini.francesco at gmail.com
CC: rbaer at atsu.edu; r-help at r-project.org

First you have to create something (e.g., a list) that holds your  
output:

mylist<-NULL

Then you loop through the levels of c and run a regression of a  
onto b
(no need to include c anymore because c will have zero variance  
within
each level of c):
for(i in levels(c)){
 temp.data<-mydataset[mydataset$c %in% i]
 mylist[[i]]<-lm(a ~  b, data=temp.data)
}

Once you are done - you can write another loop (this time across all
elements of mylist - that will have as many elements as there are
levels in c) and extract the coefficients.
Dimitri


On Fri, May 20, 2011 at 9:57 AM, Francesco Nutini
<nutini.francesco at gmail.com> wrote:

Yes Dimitri that's what I mean!
Something like this?

for(i in levels(c)) { lm(a ~  b *  c , data=mydataset)}

And what about to see the output?

Thanks!

Date: Fri, 20 May 2011 09:46:08 -0400
Subject: Re: [R] [r] regression coefficient for different factors
From: dimitri.liakhovitski at gmail.com
To: nutini.francesco at gmail.com
CC: rbaer at atsu.edu; r-help at r-project.org

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

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--
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com

-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com

		 	   		
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