Dear jayuan2008,

See ?subset. If I understand your description below, something like this
could do the job:

a1<-data.frame(x=c("a","b","a","b","a"),y=c(4,3,6,1,2))
subset(a1,y>2)
 x y
1 a 4
2 b 3
3 a 6


BTW, I think that the final result you described in your post is incorrect.


HTH,

Jorge



On Sun, Aug 31, 2008 at 2:19 AM, Yuan Jian <jayuan2008@yahoo.com> wrote:

> Hi,
>
> I have a matrix.
> >a<-cbind(c("a","b","a"),c(4,3,6))
>      [,1] [,2]
> [1,] "a"  "4"
> [2,] "b"  "3"
> [3,] "a"  "6"
>
> I want to remove rows in matrix a whose first column has frequency less
> than 2.
> in about example matrix a becomes
>      [,1] [,2]
> [1,] "a"  "4"
> [2,] "a"  "6"
>
>
>
>
>
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>
>
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