Hi
I just discovered the answer thanks to a previous thread from Peter Daalgart
The command is:
sapply(test, "[[", "statistic")
Cheers, Daniel
----- Original Message -----
To: r-help@r-project.org
Subject: extracting values from a "by" function
Date: Sun, 6 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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