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!!
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