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Naresh Gurbuxani

2016-Jun-18 22:12 UTC

[R] better loop for simulation

I want to calculate a function many times over.  My solution below works, but
does not seem very elegant.

# my function to run many times over
stud.score <- function(n.questions, mult.choice = 2) {
	prob.success <- 1 / mult.choice
	answers <- (runif(n.questions) < prob.success)
	return(sum(answers))
} 

# my method to run above function 1000 times and store results
count.df <- data.frame(n.count = rep(10, 1000))
scores.df <- apply(count.df, 1, function(x) return(stud.score(x)))	

Creating a data frame just to repeat the the count seems wasteful.  How can I
generate scores.df without count.df?

Thanks,
Naresh

jim holtman

2016-Jun-18 22:33 UTC

head link

[R] better loop for simulation

use replicate:
> stud.score <- function(n.questions, mult.choice = 2) {+          prob.success <- 1 / mult.choice
+          answers <- (runif(n.questions) < prob.success)
+          return(sum(answers))
+  }>
> # create 1000 results
> result <- replicate(1000, stud.score(10))
>
> # look at histogram
> stem(result)  The decimal point is at the |
   0 | 0
   1 | 0000000000000
   2 | 000000000000000000000000000000000000000000000000000000000
   3 |
00000000000000000000000000000000000000000000000000000000000000000000+26
   4 |
00000000000000000000000000000000000000000000000000000000000000000000+116
   5 |
00000000000000000000000000000000000000000000000000000000000000000000+153
   6 |
00000000000000000000000000000000000000000000000000000000000000000000+142
   7 |
00000000000000000000000000000000000000000000000000000000000000000000+35
   8 | 00000000000000000000000000000000000000000000
   9 | 000000000000
  10 | 0


Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

On Sat, Jun 18, 2016 at 6:12 PM, Naresh Gurbuxani <
naresh_gurbuxani at hotmail.com> wrote:
> I want to calculate a function many times over.  My solution below works,
> but does not seem very elegant.
>
> # my function to run many times over
> stud.score <- function(n.questions, mult.choice = 2) {
>         prob.success <- 1 / mult.choice
>         answers <- (runif(n.questions) < prob.success)
>         return(sum(answers))
> }
>
> # my method to run above function 1000 times and store results
> count.df <- data.frame(n.count = rep(10, 1000))
> scores.df <- apply(count.df, 1, function(x) return(stud.score(x)))
>
> Creating a data frame just to repeat the the count seems wasteful.  How
> can I generate scores.df without count.df?
>
> Thanks,
> Naresh
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>
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Duncan Murdoch

2016-Jun-18 23:24 UTC

head link

[R] better loop for simulation

On 18/06/2016 6:12 PM, Naresh Gurbuxani wrote:> I want to calculate a function many times over.  My solution below works,
but does not seem very elegant.
>
> # my function to run many times over
> stud.score <- function(n.questions, mult.choice = 2) {
> 	prob.success <- 1 / mult.choice
> 	answers <- (runif(n.questions) < prob.success)
> 	return(sum(answers))
> }
>
> # my method to run above function 1000 times and store results
> count.df <- data.frame(n.count = rep(10, 1000))
> scores.df <- apply(count.df, 1, function(x) return(stud.score(x)))	
>
> Creating a data frame just to repeat the the count seems wasteful.  How can
I generate scores.df without count.df?
>
> Thanks,
You don't need a data frame or a loop at all.  You're simulating 
binomial values, and R has rbinom() to do that in a vectorized way.

Duncan

Dalthorp, Daniel

2016-Jun-18 23:31 UTC

head link

[R] better loop for simulation

try:

n.questions <- 10  # or however many you want
mult.choice <- 2
scores <- rbinom(1000, size = n.questions, prob = 1/mult.choice)


On Sat, Jun 18, 2016 at 3:12 PM, Naresh Gurbuxani <
naresh_gurbuxani at hotmail.com> wrote:
> I want to calculate a function many times over.  My solution below works,
> but does not seem very elegant.
>
> # my function to run many times over
> stud.score <- function(n.questions, mult.choice = 2) {
>         prob.success <- 1 / mult.choice
>         answers <- (runif(n.questions) < prob.success)
>         return(sum(answers))
> }
>
> # my method to run above function 1000 times and store results
> count.df <- data.frame(n.count = rep(10, 1000))
> scores.df <- apply(count.df, 1, function(x) return(stud.score(x)))
>
> Creating a data frame just to repeat the the count seems wasteful.  How
> can I generate scores.df without count.df?
>
> Thanks,
> Naresh
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>


-- 
Dan Dalthorp, PhD
USGS Forest and Rangeland Ecosystem Science Center
Forest Sciences Lab, Rm 189
3200 SW Jefferson Way
Corvallis, OR 97331
ph: 541-750-0953
ddalthorp at usgs.gov

	[[alternative HTML version deleted]]

Naresh Gurbuxani

2016-Jun-19 03:15 UTC

head link

[R] better loop for simulation

Daniel, Duncan, and Jim,


Many thanks for your prompt responses.  My example function is indeed binomial,
for which a built function already exists.  But my goal is to find a general
solution which would work for other functions as well.

replicate() works well for me.

Naresh
________________________________
From: Dalthorp, Daniel <ddalthorp at usgs.gov>
Sent: Saturday, June 18, 2016 7:31 PM
To: Naresh Gurbuxani
Cc: R-help at r-project.org
Subject: Re: [R] better loop for simulation

try:

n.questions <- 10  # or however many you want
mult.choice <- 2
scores <- rbinom(1000, size = n.questions, prob = 1/mult.choice)


On Sat, Jun 18, 2016 at 3:12 PM, Naresh Gurbuxani <naresh_gurbuxani at
hotmail.com<mailto:naresh_gurbuxani at hotmail.com>> wrote:
I want to calculate a function many times over.  My solution below works, but
does not seem very elegant.

# my function to run many times over
stud.score <- function(n.questions, mult.choice = 2) {
        prob.success <- 1 / mult.choice
        answers <- (runif(n.questions) < prob.success)
        return(sum(answers))
}

# my method to run above function 1000 times and store results
count.df <- data.frame(n.count = rep(10, 1000))
scores.df <- apply(count.df, 1, function(x) return(stud.score(x)))

Creating a data frame just to repeat the the count seems wasteful.  How can I
generate scores.df without count.df?

Thanks,
Naresh
______________________________________________
R-help at r-project.org<mailto:R-help at r-project.org> mailing list -- To
UNSUBSCRIBE and more, see
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.



--
Dan Dalthorp, PhD
USGS Forest and Rangeland Ecosystem Science Center
Forest Sciences Lab, Rm 189
3200 SW Jefferson Way
Corvallis, OR 97331
ph: 541-750-0953
ddalthorp at usgs.gov<mailto:ddalthorp at usgs.gov>


	[[alternative HTML version deleted]]

R help - Jun 2016 - better loop for simulation

[R] better loop for simulation

[R] better loop for simulation

[R] better loop for simulation

[R] better loop for simulation

[R] better loop for simulation