[R] issue creating a subset

[Jim Lemon]

On 03/01/2013 12:53 PM, Pablo Menese wrote:
> I'm performing item response theory with eRm packages
> I am excluding the persons that doesn't fit in the infit/outfit persons.
> for that I created a condition. then I have to create a new subset or
> matrix but with the condition.
>
> So:
>
> ORIGINAL
>
> matrix<-cbind(item1, item2, item3, item4)
>
> IF I PERFORM A head(matrix)
>
> item1 item2 item3 item4
>    3         2       3       1
>    3         1       2       4
>
> THEN I CREATE THE LOGIC CONDITION
>
> z<-thing==T
>
> THEN I TRY TO CREATE THE NEW MATRIX BUT WITH THE CONDITION
>
> matrix2<-cbind(item1[z==T], item2[z==T], item3[z==T], item4[z==T])
>
> THE ISSUE IS THAT IF I PERFORM A head(matrix2)
>
>   I1        I2       I3      I4
>    3         2       3       1
>    3         1       2       4
>
> The names of the columns change at all.
>
> CAN ANYONE HELP ME TO KEEP THE SAME NAMES?
>
Hi Pablo,
If I understand what you are doing, you are "taking the scenic route". 
Say you have a matrix of scores:

scoremat<-matrix(sample(1:4,40,TRUE),ncol=4)

and a vector specifying whether each person is in or out:

z<-sample(c(TRUE,FALSE),10,TRUE)

all you have to do is:

scoremat2<-scoremat2[z,]

Jim