[R] better loop for simulation

[Naresh Gurbuxani]

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
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Dan Dalthorp, PhD
USGS Forest and Rangeland Ecosystem Science Center
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