predict.glm

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Maurice,

The 'newdata' argument should be a data.frame with the
same names as used for your predictors in the glm formula.

For the data you quote below (after fixing the missing y1),
try:

yhat <- predict(reg1, newdata = data.frame(x1 = x2))
length(yhat)
[1] 200

A careful reading of ?predict would have told you that:

"newdata    optionally, a data frame in which to look for
             variables with which to predict."

If that is not your problem, perhaps you could give an
example with data and code that illustrates your problem.

  -Peter Ehlers
Hi,

See below I reply your message for <https://stat.ethz.ch/pipermail/r-help/2008-April/160966.html>[R] predict.glm & newdata posted on Fri Apr 4 21:02:24 CEST 2008 

You say  it ##works fine but it does not: if you look at the length of yhat2, you will find 100 and not 200 as expected. In fact predict(reg1, data=x2) gives the same results as predict(reg1).

So I am still looking for a solution of this problem.

best regards

Maurice 

===========

Hi,

could it be the "newdata" argument? When I run predict with the newdata
argument, I get an error message - a different one though. The second reason
might be that your dataset is named df, which is defined as a function an
may produce problems. Try renaming the dataset.

yhat=predict(reg1,newdata=x2) 

x1=seq(1:100)           
r.norm1=rnorm(100,0,20) 
x1=r.norm1+x1           

x2=x1*2                 
r.norm2=rnorm(200,0,20) 
x2=r.norm2+x2

reg1=glm(y1~x1,binomial)      
yhat=predict(reg1)                   ##prediction works fine           
yhat=predict(reg1,newdata=x2) ##gives error message because of "newdata"

Error in eval(predvars, data, env) : 
  numeric 'envir' arg not of length one

yhat=predict(reg1,data=x2) ##works fine

##using offset

ofst=rep(0.5,100)                    

reg1=glm(y1~x1,binomial,offset=ofst) 
yhat=predict(reg1)                   
yhat1=predict(reg1,newdata=x2) ##gives error message       
yhat2=predict(reg1,data=x2)      ##works fine  

% ================================================= 
% Maurice CHARBIT
% Ecole Nationale Sup?rieure des T?l?communications
% D?partement TSI 
% 37,39 rue Dareau, pi?ce A321
% 75634 - PARIS cedex 13 FRANCE
% email: maurice.charbit at telecom-paristech.fr    
% Fax:   (33) (0)1 45 81 71 44
% Phone: (33) (0)1 45 81 71 78
%==================================================| 
	[[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.

Peter Ehlers
University of Calgary
403.202.3921

Hi,

See below I reply your message for <https://stat.ethz.ch/pipermail/r-help/2008-April/160966.html 
[R] predict.glm & newdata posted on Fri Apr 4 21:02:24 CEST 2008

You say  it ##works fine but it does not: if you look at the length  
of yhat2, you will find 100 and not 200 as expected. In fact  
predict(reg1, data=x2) gives the same results as predict(reg1).

So I am still looking for a solution of this problem.
You are replying to a posting that is almost two years old. The  
posting back then was incomplete in that y1 was never defined. Why not  
post a more complete and updated question?
David.
>
>
> best regards
>
> Maurice
>
> ===========
>
> Hi,
>
> could it be the "newdata" argument? When I run predict with the  
> newdata
> argument, I get an error message - a different one though. The  
> second reason
> might be that your dataset is named df, which is defined as a  
> function an
> may produce problems. Try renaming the dataset.
>
> yhat=predict(reg1,newdata=x2)
>
> x1=seq(1:100)
> r.norm1=rnorm(100,0,20)
> x1=r.norm1+x1
>
> x2=x1*2
> r.norm2=rnorm(200,0,20)
> x2=r.norm2+x2
>
> reg1=glm(y1~x1,binomial)
> yhat=predict(reg1)                   ##prediction works fine
> yhat=predict(reg1,newdata=x2) ##gives error message because of  
> "newdata"
>
>> Error in eval(predvars, data, env) :
>  numeric 'envir' arg not of length one
>
> yhat=predict(reg1,data=x2) ##works fine
>
> ##using offset
>
> ofst=rep(0.5,100)
>
> reg1=glm(y1~x1,binomial,offset=ofst)
> yhat=predict(reg1)
> yhat1=predict(reg1,newdata=x2) ##gives error message
> yhat2=predict(reg1,data=x2)      ##works fine
>
>
> % =================================================
> % Maurice CHARBIT
> % Ecole Nationale Sup?rieure des T?l?communications
> % D?partement TSI
> % 37,39 rue Dareau, pi?ce A321
> % 75634 - PARIS cedex 13 FRANCE
> % email: maurice.charbit at telecom-paristech.fr
> % Fax:   (33) (0)1 45 81 71 44
> % Phone: (33) (0)1 45 81 71 78
> %==================================================|
> 	[[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.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT