From: David Schwab <dvschwab46225_at_gmail.com>

Date: Fri, 02 May 2008 10:19:09 -0400

R-help_at_r-project.org mailing list

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. Received on Fri 02 May 2008 - 14:21:54 GMT

Date: Fri, 02 May 2008 10:19:09 -0400

Category Value1 Value2 1 .5 .8 1 .3 .9 . . . . . . . . . 2 1.4 1.3 2 1.3 1.3 . . . . . . . . . 15 .2 .3 15 .5 .1

So in all there are 15 categories, and each category contains two sets of observations which I want to compare. I only want to compare Value1 and Value2 within each category, but I need to do it 15 times (once for each category), so I wanted to write an R function to make it easier.

Right now I am using a for() loop to do the comparison. My loop looks like this:

for(i in 1:21)

*{
*

x <- t.test(Value1[Category == i], Value2[Category == i])

y <- c(y, x$p.value)

}

The loop runs and everything is working well. However, I am not sure how to translate this code into a function. In particular, I'm not sure how to write a function that passes a data frame ds (containing Category, Value1, and Value2 as members) as an argument, and then accessing these members within the body of the function. I've tried the following:

repeated_test <- function(data)

*{
*

for(i in 1:21)

{

x <- t.test(ds$Value1[ds$Category == i], ds$Value2[ds$Category == i])

y <- c(y, x$p.value)

}

This will run, but only if the members of the data frame I am passing as an argument are in fact named Value1, Value2, and Category. This is fine for now, but in the future I will have to run this function on data where I cannot be sure this is the case. Rather than change the member names by hand, I would like to make the function generic to work with any data frame. How do I do this? Or is there a better way to do this without the for() loop (for example, using apply())?

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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. Received on Fri 02 May 2008 - 14:21:54 GMT

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