Where you have
result[1]$p.value
result[2]$p.value
You need
result[[1]]$p.value
result[[2]]$p.value
to get the first component of the list.
Sarah
On Fri, Jun 12, 2020 at 5:35 PM Sorkin, John <jsor...@som.umaryland.edu> wrote:
>
> Colleagues,
> I am trying to retrieve the p values produced by a Student's t-test run using
> a by function, but can not do so. I can easily get the p value when I run s
> Student's t-test without a by function. What is the secret to obtaining
> results returned from a function run within a by function.
>
> An annotated repeatable example (including data) can be found below.
> Thank you,
> John
>
>
> # Test data
> mydata <- structure(list(Group = structure(c(2L, 1L, 2L, 2L, 1L, 2L, 1L,
> 2L, 2L, 1L, 2L, 1L, 2L), .Label = c("EPA", "P"), class = "factor"),
> WtBaseline = c(76.6, 73.8, 77.6, 91.7, 110.3, 121.7, 82.1,
> 82.8, 119, 88.4, 75.7, 71.4, 72.1)), class = "data.frame",
> row.names = c(NA,-13L))
>
> cat("This is what mydata looks like\n")
> mydata
>
> result <- by(mydata$WtBaseline,mydata$Group,t.test)
> cat("Student's t-test run using by command\n")
> cat("Result has results for both groups, EPA and P\n")
> result
>
> cat("I can isolate the collective results for group EPA\n")
> result[1]
> cat("I can isolate the collective results for group P\n")
> result[2]
>
> cat("I cant get the p-values for the gruops")
> result[1]$p.value
> result[2]$p.value
>
> cat("When run without by function, one can get the p value\n")
> xxx <- t.test(WtBaseline~Group,data=mydata)
> cat("t-test run without by fundtion\n")
> xxx
> cat("p value isolated from t-test run without by function\n")
> xxx$p.value
>
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
> Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
>
> [[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.
--
Sarah Goslee (she/her)
http://www.numberwright.com
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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