R help - Feb 2010 - Problems with looping in R

Dear R Experts,
This is my R function. 

 
my<-function(servername,dbname,dbtable){
 	library(RODBC)
 	channel<- odbcDriverConnect(paste("driver=SQL
Server;server=",servername))
 	init_data<- sqlQuery(channel,paste("select *
from",dbname,"..",dbtable))
 	init_data <- subset(init_data,!is.null(init_data[,1]),)
	print(dim(init_data))
	unique_b_vals = unique(init_data[,3])
	print(unique_b_vals)
	final_set <- NULL
	for(b_val in unique_b_vals)	
	{
		temp1 = subset(init_data,init_data[,3] == b_val,)
		temp1 = temp1[sample(dim(temp1)[1], 200),]
		if (is.null(final_set))
		{
			final_set <<- temp1
		}
		else 
			final_set <<- rbind(final_set,temp1)
		
	}
}

Here What I am doing is connecting to MS sql Server through R and extracting 
the data and init_data contains all my data matrix. After getting all the
data in init_data I want to randomly select data of size say 200. when I am
doing this directly from the command line and not through this function the
for loop runs well and gives me the sample data. But when I try to put this
in a function the loop is failing and does not contain any data.I debugged
the code init_data contains data but final_set does not contain any data. 
The appending is not working when i put this in a function but the same code
works fine without a function
Any solution for this? Please Help
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vikrant wrote:
> 
>  
> my<-function(servername,dbname,dbtable){
> ...
> 	final_set <- NULL
> 	for(b_val in unique_b_vals)	
> 	{
> 		temp1 = subset(init_data,init_data[,3] == b_val,)
> 		temp1 = temp1[sample(dim(temp1)[1], 200),]
> 		if (is.null(final_set))
> 		{
> 			final_set <<- temp1
> 		}
> 		else 
> 			final_set <<- rbind(final_set,temp1)
> 		
> 	}
> }
> 
> When I am doing this directly from the command line and not through this
> function the for loop runs well and gives me the sample data. But when I
> try to put this in a function the loop is failing and does not contain any
> data.I debugged the code init_data contains data but final_set does not
> contain any data. 
> 
Remove all <<-, these are harmful for your health and should be used by
trained neurosurgeons only. Add

final_set 

(think of "return(final_set)")

as the last line of your function, and use the function return in your
calling part.

As an aside: Avoid "select *", use select (primary key) where ... is
not
null instead, and do the sampling on the primary keys.

Dieter






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Thanks Dieter. It works.
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