[R] extracting values from a "by" function

From: Daniel Stahl <daniel_stahl_at_operamail.com>
Date: Sun, 06 Jul 2008 05:59:04 +0800


Hello,

I am trying to extract t and pvalues from a 1000 ttests using the by-function but everythinhg I tried did not work. Unfortunately googling "by" is not very helpful. Any help will be very appreciated. Cheers,
Danile Stall

*creating a data set
library(MASS)
dataset <- mvrnorm(160, mu, Sigma)
dataset <- as.data.frame(dataset)
dataset$GROUP <- rep(1:10, each=16)
data.uni <- reshape(df, varying = list(c("V1","V2")), v.names="Y",direction="long") *the actual tests:
test<-by(data.uni, data.uni$GROUP, function(x)t.test(Y ~ time, data = x, paired = TRUE)) *in case this will help you:
summary(test)
str(test)

> summary(test)

   Length Class Mode

1  9      htest list
2  9      htest list
3  9      htest list
4  9      htest list
5  9      htest list
6  9      htest list
7  9      htest list
8  9      htest list
9  9      htest list
10 9      htest list

> str(test)

List of 10
 $ 1 :List of 9
..$ statistic : Named num -4.26

  .. ..- attr(*, "names")= chr "t"

..$ parameter : Named num 15
  .. ..- attr(*, "names")= chr "df"

..$ p.value : num 0.000682
..$ conf.int : atomic [1:2] -3.13 -1.04
  .. ..- attr(*, "conf.level")= num 0.95

..$ estimate : Named num -2.09
  .. ..- attr(*, "names")= chr "mean of the differences"

..$ null.value : Named num 0
  .. ..- attr(*, "names")= chr "difference in means"

..$ alternative: chr "two.sided"
..$ method : chr "Paired t-test"
..$ data.name : chr "Y by time"

  ..- attr(*, "class")= chr "htest"
 $ 2 :List of 9
-- 

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Received on Sat 05 Jul 2008 - 22:03:55 GMT

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