R help - Jan 2009 - looping over a string

Hi list,

I'm using R 2.8.1 under Windows vista. I have the following problem:

First of all I create a string-vector. Then I "convert" these strings 
into variables and assign a vector of numeric values. So far 
everything's fine.
Now I want to do nearly the same again: I create another string-vector 
and I want to assign the variance. So I have to loop over the first 
string-vector.
But this does not work unfortunately. I looked in the R-list-search but 
I cannot find the right answer.

Please find enclosed the pseudo-code:

#Tage zwischen berechnung und 31.03.2009
Berechnung<-as.Date("22.01.2009","%d.%m.%Y")
Enddatum<-as.Date("31.03.2009","%d.%m.%Y")
Tage<-difftime(Enddatum, Berechnung)
Tage<-as.numeric(substr(format(Tage),1,2))

#maximal interessierend sind 100 Tage (4 Monate)-Differenzen
max_int<-82
Tage<-max_int
max_bob<-82

varnames<-paste("st_rendite_",seq(max_int),sep="")
analyse<-rnorm(10000)
for(i in 1:min(max_bob,max_int)){
  assign(varnames[i],diff(log(analyse),i)*100)
}

#Wurzel_t - Approximation ?berpr?fen
varianzen<-paste("var_",seq(Tage),sep="")
for(i in 1:Tage){
#in this line is the error I cannot handle (st_rendite_i):
  assign(varianzen[i],var(st_rendite_i)/100^2)
}

Thanks for your help,
Thomas

I don't see right off why the one works and the other doesn't, but this
looks like one of those cases that would be better done using a list rather than
global variables.

Instead of assigning the variables in the global workspace, create a list and
assign them there.  Then you can use lapply instead of a loop and you avoid the
potential pitfalls associated with globals.

Hope this helps,

-- 
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 Thomas Schwander
> Sent: Thursday, January 22, 2009 12:38 PM
> To: r-help at r-project.org
> Subject: [R] looping over a string
> 
> Hi list,
> 
> I'm using R 2.8.1 under Windows vista. I have the following problem:
> 
> First of all I create a string-vector. Then I "convert" these
strings
> into variables and assign a vector of numeric values. So far
> everything's fine.
> Now I want to do nearly the same again: I create another string-vector
> and I want to assign the variance. So I have to loop over the first
> string-vector.
> But this does not work unfortunately. I looked in the R-list-search but
> I cannot find the right answer.
> 
> Please find enclosed the pseudo-code:
> 
> #Tage zwischen berechnung und 31.03.2009
> Berechnung<-as.Date("22.01.2009","%d.%m.%Y")
> Enddatum<-as.Date("31.03.2009","%d.%m.%Y")
> Tage<-difftime(Enddatum, Berechnung)
> Tage<-as.numeric(substr(format(Tage),1,2))
> 
> #maximal interessierend sind 100 Tage (4 Monate)-Differenzen
> max_int<-82
> Tage<-max_int
> max_bob<-82
> 
> varnames<-paste("st_rendite_",seq(max_int),sep="")
> analyse<-rnorm(10000)
> for(i in 1:min(max_bob,max_int)){
>   assign(varnames[i],diff(log(analyse),i)*100)
> }
> 
> #Wurzel_t - Approximation ?berpr?fen
> varianzen<-paste("var_",seq(Tage),sep="")
> for(i in 1:Tage){
> #in this line is the error I cannot handle (st_rendite_i):
>   assign(varianzen[i],var(st_rendite_i)/100^2)
> }
> 
> Thanks for your help,
> Thomas
> 
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