

Here are the code and results
============
> a=matrix(1:20,5)
> a
     [,1] [,2] [,3] [,4]
[1,]    1    6   11   16
[2,]    2    7   12   17
[3,]    3    8   13   18
[4,]    4    9   14   19
[5,]    5   10   15   20
> colnames(a)=c("A","AB","C","CD")
> a
     A AB  C CD
[1,] 1  6 11 16
[2,] 2  7 12 17
[3,] 3  8 13 18
[4,] 4  9 14 19
[5,] 5 10 15 20
> group=factor(substring(colnames(a),1,1))
> group
[1] A A C C
Levels: A C
> a[,levels(group)=="A"]
     A  C
[1,] 1 11
[2,] 2 12
[3,] 3 13
[4,] 4 14
[5,] 5 15
> a[,levels(group)=="C"]
     AB CD
[1,]  6 16
[2,]  7 17
[3,]  8 18
[4,]  9 19
[5,] 10 20

==============
But, I was expect that:
a[,levels(group)=="A"]
     A  AB
[1,] 1 6
[2,] 2 7
[3,] 3 8
[4,] 4 9
[5,] 5 10

Could anybody explain why? Thanks a lot!!
	[[alternative HTML version deleted]]

