R help - Oct 2008 - For loop - how to assign "i" when it is not an element of an index?

Hello,

I'm trying to build a for loop, where I estimate a series of models with
different sets of (time series) data.
However my for loop doesn't recognize the "i" 

##################### code################
window.1=anomalies.CAK[(positions(anomalies.CAK)>=timeDate("1/1/1971")
&
positions(anomalies.CAK)<=timeDate("6/30/1991") )]
....
window.14=anomalies.CAK[(positions(anomalies.CAK)>=timeDate("1/1/1984")
&
positions(anomalies.CAK)<=timeDate("6/30/2004") ),]

for (i in 1:14){
	ar1mods[1] = lm ( formula = window.i~ ar(1) )
}
################################# end code ###################

Problem: Object "window.i" not found 

Anybody have a quick tip on what I'm doing wrong?

-- 
View this message in context:
http://www.nabble.com/For-loop---how-to-assign-%22i%22-when-it-is-not-an-element-of-an-index--tp20083917p20083917.html
Sent from the R help mailing list archive at Nabble.com.

Scotty Nelson <poorboy44 <at> hotmail.com> writes:
> I'm trying to build a for loop, where I estimate a series of models
with
> different sets of (time series) data.
> However my for loop doesn't recognize the "i" 
> 
> ##################### code################
>
window.1=anomalies.CAK[(positions(anomalies.CAK)>=timeDate("1/1/1971")
&
> positions(anomalies.CAK)<=timeDate("6/30/1991") )]
> ....
>
window.14=anomalies.CAK[(positions(anomalies.CAK)>=timeDate("1/1/1984")
&
> positions(anomalies.CAK)<=timeDate("6/30/2004") ),]
> 
> for (i in 1:14){
> 	ar1mods[1] = lm ( formula = window.i~ ar(1) )
> }
The easiest would be to put the selection of the cases into the loop, and always
use the same formula. You could also use
formula=paste("window.",i,sep=""). That
approach will work for the simple example, but you might run into eval-problems
later (though probably not for lm). 

# B.D. Ripley val(subst) workaround
#http://finzi.psych.upenn.edu/R/Rhelp02a/archive/16599.html


Dieter

1. Thanks for the reproducible example. It makes the issue clear.

2. Your error reflects a profound confusion about how programming works in
general, and R in particular.  I think the following is a correct technical
explanation (I am not a trained programmer, so corrections from those who
are would be appreciated).

R is not a macro language. The "i" in "for( i in 1:14)" is a
name of a
variable, not a symbol for which substitution will occur.  window.i is also
a name that **has nothing to do with the variable named "i" ** . To do
what
you want, you need to explcitly make the connection. One could do it the way
you have set things up by first composing the names of the window.i objects
and then associating the names with the objects:

... for (i in 1:14){
 ...
window.i <- get(paste("window","i",sep="."))
...
}

But this construction is clumsy. A better way to do things is to make your
windows and armods objects different components of a list and refer to them
via subscripting:

windows <- as.list(1:14)
armods <- windows
windows[[1]] <- ...
windows[[2]] <- ...
...
## warning: untested

for(i in 1:14){
	...
	armods[[i]] <- lm ( formula = window[[i]] ~ ar(1) ) 
	...
}

Use of a programming language -- any language -- requires a learning
commitment that you do not appear to have made. Please spend some quality
time with "An Introduction to R" and other R learning resources before
you
post to the list again.

-- Bert Gunter

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of Scotty Nelson
Sent: Monday, October 20, 2008 11:02 PM
To: r-help at r-project.org
Subject: [R] For loop - how to assign "i" when it is not an element of
an
index?


Hello,

I'm trying to build a for loop, where I estimate a series of models with
different sets of (time series) data.
However my for loop doesn't recognize the "i" 

##################### code################
window.1=anomalies.CAK[(positions(anomalies.CAK)>=timeDate("1/1/1971")
&
positions(anomalies.CAK)<=timeDate("6/30/1991") )]
....
window.14=anomalies.CAK[(positions(anomalies.CAK)>=timeDate("1/1/1984")
&
positions(anomalies.CAK)<=timeDate("6/30/2004") ),]

for (i in 1:14){
	ar1mods[1] = lm ( formula = window.i~ ar(1) )
}
################################# end code ###################

Problem: Object "window.i" not found 

Anybody have a quick tip on what I'm doing wrong?

-- 
View this message in context:
http://www.nabble.com/For-loop---how-to-assign-%22i%22-when-it-is-not-an-ele
ment-of-an-index--tp20083917p20083917.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
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.