R help - Jan 2011 - Looping with incremented object name and increment function

Folks,

I am trying to get a loop to run which increments the object name as part of
the loop.  Here "fit1" "fit2" "fit3" and
"fit4" are linear regression models
that I have created.
> for (ii in c(1:4)){
+ SSE[ii]=rbind(anova(fit[ii])$"Sum Sq")
+ dfe[ii]=rbind(summary(fit[ii])$df)
+ }
Error in anova(fit[ii]) : object 'fit' not found

Why isn't it looking for object 'fit1' instead of 'fit'?

The idea is that it would store in SSE1 the Sum Sq of the model fit1, and so
on for the other 3 models.  Is there a way to do this in R?  I can do it in
Stata, but am only somewhat knowledgeable in R.

-Michael

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This is FAQ 7.21.

The real gem in the answer there is at the end where it tells you that it is
easier to just use a list.  If your fit1, fit2, fit3, and fit4 were elements in
a list then you can just loop through the list elements, or even easier use the
lapply function to loop through the list elements for you.

The syntax fit[ii] means that you want the ii'th element of the vector named
"fit", the FAQ shows how to do what you want, but in the long run (and
the medium run, and even the short run) using a list instead of separate global
variables will make your life easier.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Michael Costello
> Sent: Friday, January 21, 2011 9:43 AM
> To: r-help at r-project.org
> Subject: [R] Looping with incremented object name and increment
> function
> 
> Folks,
> 
> I am trying to get a loop to run which increments the object name as
> part of
> the loop.  Here "fit1" "fit2" "fit3" and
"fit4" are linear regression
> models
> that I have created.
> 
> > for (ii in c(1:4)){
> + SSE[ii]=rbind(anova(fit[ii])$"Sum Sq")
> + dfe[ii]=rbind(summary(fit[ii])$df)
> + }
> Error in anova(fit[ii]) : object 'fit' not found
> 
> Why isn't it looking for object 'fit1' instead of
'fit'?
> 
> The idea is that it would store in SSE1 the Sum Sq of the model fit1,
> and so
> on for the other 3 models.  Is there a way to do this in R?  I can do
> it in
> Stata, but am only somewhat knowledgeable in R.
> 
> -Michael
> 
> 	[[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.

Hi:

Here's an example of how to extract pieces from model objects using the plyr
package. I'm using the attitude data set from the datasets package
(autoloaded).

# Generate four models
m1 <- lm(rating ~ ., data = attitude)
m2 <- lm(rating ~ complaints + learning, data = attitude)
m3 <- lm(rating ~ complaints * learning, data = attitude)
m4 <- lm(rating ~ complaints, data = attitude)
# Combine them into a list
mlist <- list(m1 = m1, m2 = m2, m3 = m3, m4 = m4)

# Utility functions:
# In this context, x represents a generic model object. We want
# to extract the same information from each object.
# Can package these (or others) into a single function if you
# wish to output a list object.

# Sums of squares extraction:
ss <- function(x) summary(x)$coefficients[, 2]

# R^2
r2 <- function(x) summary(x)$r.squared

# Model and residual df:
dfs <- function(x) summary(x)$df[1:2]

# ldply() takes a list object as input and returns a data frame object
# llply() takes a list object as input and returns a list
# Each call applies a utility function to each component model in the list
library(plyr)
ldply(mlist, r2)
ldply(mlist, dfs)
llply(mlist, ss)

HTH,
Dennis

On Fri, Jan 21, 2011 at 8:42 AM, Michael Costello <
michaelavcostello@gmail.com> wrote:
> Folks,
>
> I am trying to get a loop to run which increments the object name as part
> of
> the loop.  Here "fit1" "fit2" "fit3" and
"fit4" are linear regression
> models
> that I have created.
>
> > for (ii in c(1:4)){
> + SSE[ii]=rbind(anova(fit[ii])$"Sum Sq")
> + dfe[ii]=rbind(summary(fit[ii])$df)
> + }
> Error in anova(fit[ii]) : object 'fit' not found
>
> Why isn't it looking for object 'fit1' instead of
'fit'?
>
> The idea is that it would store in SSE1 the Sum Sq of the model fit1, and
> so
> on for the other 3 models.  Is there a way to do this in R?  I can do it in
> Stata, but am only somewhat knowledgeable in R.
>
> -Michael
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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]]