Thank you for all your responses, I assure you this is not homework.  I am
a graduate student and my classes are complete.  I am trying multiple
different ways to analyze data and my lab requests different types of
scripts to accomplish various tasks.  I am the most computer savy in the
lab so it comes to me.  I am continually trying to learn more about using R
and I truly value all the suggestions.  Again, thank you for your
assistance,

Regards,
Charles

On Fri, Oct 19, 2012 at 8:30 AM, Terry Therneau <therneau@mayo.edu> wrote:

> The number of recent questions from umn.edu makes me wonder if there's
> homework involved....
>
> Simpler for your example is to use get and subset.
> dat <- structure(.....    as found below
> var.to.test <- names(dat)[4:6]   #variables of interest
> nvar <- length(var.to.test)
> chisq <- double(nvar)
> for (i in 1:nvar) {
>     tfit <- survdiff(Surv(time, completion==2) ~ get(var.to.test[i]),
> data=dat, subset=(group==3))
>     chisq[i] <- tfit$chisq
>     }
> write.csv(data.frame(var.to.**test, chisq))
>
> On 10/19/2012 05:00 AM, r-help-request@r-project.org wrote:
>
>> Hello,
>>
>> I am trying to set up a loop that can run the survdiff function with the
>> ultimate goal to generate a csv file with the p-values reported.  However,
>> whenever I try a loop I get an error such as "invalid type (list) for
>> variable 'survival_data_variables[i]".
>>
>> This is a subset of my data:
>>
>> structure(list(time = c(1.51666666666667, 72, 72, 25.7833333333333,
>> 72, 72, 72, 72, 72, 72, 1.18333333333333, 0.883333333333333,
>> 1.15, 0.866666666666667, 72, 1.03333333333333, 72, 1.05, 72,
>> 22.7666666666667), group = c(2L, 1L, 3L, 3L, 3L, 4L, 4L,
>> 1L, 3L, 3L, 3L, 3L, 4L, 3L, 3L, 4L, 3L, 4L, 3L, 4L), completion =
>> structure(c(2L,
>> 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 2L, 1L,
>> 2L, 1L, 2L), .Label = c("1", "2"), class = "factor"), var1 =
>> structure(c(2L,
>> 2L, 3L, 1L, 1L, 3L, 1L, 1L, 1L, 3L, 2L, 2L, 4L, 3L, 2L, 4L, 2L,
>> 4L, 2L, 4L), .Label = c("1", "2", "3", "4"), class = "factor"),
>>      var2 = structure(c(3L, 3L, 1L, 1L, 2L, 4L, 3L,
>>      3L, 2L, 4L, 2L, 1L, 2L, 1L, 2L, 2L, 4L, 4L, 2L, 3L), .Label = c("1",
>>      "2", "3", "4"), class = "factor"), var3 = structure(c(4L,
>>      2L, 3L, 1L, 3L, 4L, 4L, 2L, 2L, 4L, 2L, 2L, 1L, 2L, 2L, 2L,
>>      1L, 3L, 4L, 1L), .Label = c("1", "2", "3", "4"), class = "factor")),
>> .Names = c("time",
>> "group", "completion", "var1", "var2",
>> "var3"), row.names = c(NA, 20L), class = "data.frame")
>>
>>
>> The loop I have been trying for just group 3 is:
>>
>> d=data.frame()
>> for(i in 4:6){
>>      a=assign(paste("p-value",i,**sep=""),
>>          survdiff(Surv(time, completion=="2")~dat[i],
>>          data=dat[group=="3",],
>>          rho=0))
>>      b=as.matrix(a$chisq)
>>      d=rbind(d, b)
>> write.csv(d, file="C:/.../junk.csv", quote=FALSE)}
>>
>> Perhaps I am making this more difficult than it needs to be.  Thanks for
>> any help,
>>
>> Charles
>>
>

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