On Dec 9, 2012, at 9:06 AM, 歐詠芝 wrote:
Dear all:
I have simulated ability(500 examinees) and difficulty(40 items).
as:
N <- 500
theta <- rnorm( N )
I <- 40
b <- seq( -2 , 2 , len=I )
p1 <- plogis( outer( theta, b, "-" ) )
I want to simulate 10 responses matrix
through this syntax: respR <- 1 * ( p1 > matrix( runif( N*I ) ,
nrow=N ,
ncol=I ) )
I tried this:
n<-10
respR<-list()
for(i in 1:n){
respR[[i]] <- 1 * ( p1 > matrix( runif( N*I ) , nrow=N , ncol=I ) )
}
but I didn't get 10 respR matrix, such as: respR[[1]], respR[[2]].....
I got 10 logical matrices ... just as the code specified. What were
you expecting?
> str(respR[[1]])
num [1:500, 1:40] 1 1 1 1 1 1 0 1 0 0 ...
> str(respR)
List of 10
$ : num [1:500, 1:40] 1 1 1 1 1 1 0 1 0 0 ...
$ : num [1:500, 1:40] 1 1 0 1 1 1 0 0 1 1 ...
$ : num [1:500, 1:40] 1 1 1 0 1 1 1 1 1 0 ...
$ : num [1:500, 1:40] 0 1 1 0 1 1 1 1 1 0 ...
$ : num [1:500, 1:40] 0 1 0 0 1 1 1 1 1 0 ...
$ : num [1:500, 1:40] 0 1 1 0 1 1 1 1 0 1 ...
$ : num [1:500, 1:40] 1 1 1 0 1 1 1 1 1 1 ...
$ : num [1:500, 1:40] 0 1 1 1 1 1 0 1 1 0 ...
$ : num [1:500, 1:40] 1 1 1 1 1 1 1 1 1 1 ...
$ : num [1:500, 1:40] 0 1 1 0 1 1 1 1 1 0 ...
please help me to resolve that.
thanks!
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David Winsemius, MD
Alameda, CA, USA
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