R help - Mar 2011 - Generation of random numbers in a function - (Return command)

Dear R helpers

I have following data.frame and for each product_name, I have associated mean
and standard deviation. I need to generate 1000 random no.s for each of these
products and find the respective mean and standard deviation.
 
My R code is as follows. 
 

library(plyr)
library(reshape2)
 
filtered_new <- data.frame(product_name = c("P1", "P2",
"P3", "P4", "P5"),
output_avg = c(22.71078,22.16979,21.34420,20.17421,19.83799),
output_stdev = c(23.59924,21.21430,22.01025,18.88877,18.80436))

n <- 100

myfunction_mc = function(product_name, output_avg, output_stdev)

{

product_usage_borrowing_room_mc = rnorm(n, output_avg, output_stdev)

output_avg_mc  mean(product_usage_borrowing_room_mc)
output_stdev_mc = sd(product_usage_borrowing_room_mc)

return(output_avg_mc )

}

result <- dlply(.data = filtered_new, .variables = "product_name",
.fun = function(x)
                 myfunction_mc(product_name = x$product_name, output_avg =
x$output_avg,
                 output_stdev = x$output_stdev))

result1 <- data.frame(result)

result2 <- melt(result1)

result <- data.frame(product = filtered_new$product_name, Monte_Carlo_result
= result2$value)                 

And it gives me the desired result. 


######### PROBLEM is as given below -

But if in the "myfunction_mc", in the return statement if I try to add
'output_stdev_mc'
 i.e.

myfunction_mc = function(product_name, output_avg, output_stdev)

{

product_usage_borrowing_room_mc = rnorm(n, output_avg, output_stdev)

output_avg_mc = mean(product_usage_borrowing_room_mc)
output_stdev_mc = sd(product_usage_borrowing_room_mc)

return(output_avg_mc, output_stdev_mc)            # I have added output_stdev_m

}

result <- dlply(.data = filtered_new, .variables = "product_name",
.fun = function(x)
                 myfunction_mc(product_name = x$product_name, output_avg =
x$output_avg,
                 output_stdev = x$output_stdev))

I get following error -

Error in return(output_avg_mc, output_stdev_mc) : multi-argument returns are not
permitted

Kindly
 guide.

Regards


Vincy


	[[alternative HTML version deleted]]

You can only return a single object.  You might want to create a list
if you have multiple objects:

return(list(output_avg_mc, output_stdev_mc))


On Fri, Mar 11, 2011 at 10:51 AM, Vincy Pyne <vincy_pyne at yahoo.ca>
wrote:
> Dear R helpers
>
> I have following data.frame and for each product_name, I have associated
mean and standard deviation. I need to generate 1000 random no.s for each of
these products and find the respective mean and standard deviation.
>
> My R code is as follows.
>
>
> library(plyr)
> library(reshape2)
>
> filtered_new <- data.frame(product_name = c("P1",
"P2", "P3", "P4", "P5"),
> output_avg = c(22.71078,22.16979,21.34420,20.17421,19.83799),
> output_stdev = c(23.59924,21.21430,22.01025,18.88877,18.80436))
>
> n <- 100
>
> myfunction_mc = function(product_name, output_avg, output_stdev)
>
> {
>
> product_usage_borrowing_room_mc = rnorm(n, output_avg, output_stdev)
>
> output_avg_mc > ?mean(product_usage_borrowing_room_mc)
> output_stdev_mc = sd(product_usage_borrowing_room_mc)
>
> return(output_avg_mc )
>
> }
>
> result <- dlply(.data = filtered_new, .variables =
"product_name", .fun = function(x)
> ???????????????? myfunction_mc(product_name = x$product_name, output_avg =
x$output_avg,
> ?? ??? ??? ??? ? output_stdev = x$output_stdev))
>
> result1 <- data.frame(result)
>
> result2 <- melt(result1)
>
> result <- data.frame(product = filtered_new$product_name,
Monte_Carlo_result = result2$value)
>
> And it gives me the desired result.
>
>
> ######### PROBLEM is as given below -
>
> But if in the "myfunction_mc", in the return statement if I try
to add 'output_stdev_mc'
> ?i.e.
>
> myfunction_mc = function(product_name, output_avg, output_stdev)
>
> {
>
> product_usage_borrowing_room_mc = rnorm(n, output_avg, output_stdev)
>
> output_avg_mc = mean(product_usage_borrowing_room_mc)
> output_stdev_mc = sd(product_usage_borrowing_room_mc)
>
> return(output_avg_mc, output_stdev_mc)??????????? # I have added
output_stdev_m
>
> }
>
> result <- dlply(.data = filtered_new, .variables =
"product_name", .fun = function(x)
> ???????????????? myfunction_mc(product_name = x$product_name, output_avg =
x$output_avg,
> ?? ??? ??? ??? ? output_stdev = x$output_stdev))
>
> I get following error -
>
> Error in return(output_avg_mc, output_stdev_mc) : multi-argument returns
are not permitted
>
> Kindly
> ?guide.
>
> Regards
>
>
> Vincy
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>


-- 
Jim Holtman
Data Munger Guru

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