R help - Apr 2006 - another very simple loop question

I have a dataset with 4 years of students, and normally I want to
estimate things using each individual year, so I have a for loop as
follows

for (i in 1:4){}

However, the only way I know how to calculate estimates using all four
years of data is to put the estimations outside of the loop.  Is there
anyway to make a for loop that uses all four years at once, then uses
each individual year?

Thanks,

BQ

Hi

What about some example data? I presume you could use some

apply, tapply, aggregate or similar function but without knowing what 
you **really** want to do and how your previous attempts failed it is 
hard to give any definite answer.

e.g.
mydf<-data.frame(year=sample(1:4,100,rep=T), 
student=sample(letters[1:4],100, rep=T), result=runif(100))
aggregate(mydf$result,list(year=mydf$year,student=mydf$student), 
mean)
   year student         x
1     1       a 0.4026579
2     2       a 0.4690311
...
15    3       d 0.5316301
16    4       d 0.4401949
> 
HTH
Petr



On 14 Apr 2006 at 0:09, Brian Quinif wrote:

Date sent:      	Fri, 14 Apr 2006 00:09:32 -0400
From:           	"Brian Quinif" <bquinif at gmail.com>
To:             	r-help at stat.math.ethz.ch
Subject:        	[R] another very simple loop question
> I have a dataset with 4 years of students, and normally I want to
> estimate things using each individual year, so I have a for loop as
> follows
> 
> for (i in 1:4){}
> 
> However, the only way I know how to calculate estimates using all four
> years of data is to put the estimations outside of the loop.  Is there
> anyway to make a for loop that uses all four years at once, then uses
> each individual year?
> 
> Thanks,
> 
> BQ
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
Petr Pikal
petr.pikal at precheza.cz

In marketing research, I often need to loop through highly customized
routines similar to what you described ("all" then "each,"
or
vice-versa).  My "trick" is to loop through c(as.list(x),list(x)):

data<-your_data_frame
cvar<-your_classification_varname #where cvar %in% colnames(data)

for (u in c(as.list(x<-unique(data[,cvar])),list(x))) {
local({
data<-data[is.element(data[,cvar],u),]
#all your statements here inside the local() block
})}

This runs through all my expressions once per level of the classvar, and
then once without classification.  Add statements in here to manage NA's
(if applicable) during the extraction, and you're good to go.

-Brian J. Koch
Data Manager
Decision Development Inc





-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Brian Quinif
Sent: Thursday, April 13, 2006 11:10 PM
To: r-help at stat.math.ethz.ch
Subject: [R] another very simple loop question

I have a dataset with 4 years of students, and normally I want to
estimate things using each individual year, so I have a for loop as
follows

for (i in 1:4){}

However, the only way I know how to calculate estimates using all four
years of data is to put the estimations outside of the loop.  Is there
anyway to make a for loop that uses all four years at once, then uses
each individual year?

Thanks,

BQ

______________________________________________
R-help at stat.math.ethz.ch mailing list
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PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html