Hi Peng,
Take a look at Juliet Hannah's post at
http://www.nabble.com/correct-way-to-subset-a-vector-to24412577.html#a24412577
for
some alternatives.

<http://www.nabble.com/correct-way-to-subset-a-vector-to24412577.html#a24412577>
HTH,
Jorge


On Wed, Sep 16, 2009 at 10:14 PM, Peng Yu <> wrote:

> Hi,
>
> I want to construct a data.frame 'y' by using x$x and x$y. I think
> that there might be better ways to do it (because, for example, we can
> use a_matrix[3:5,] to extract certain rows, where 'a_matrix' is a
> matrix). Can somebody let know what the best way is?
>
> > a=data.frame(x=1:10,y=rep("abc",10),z=rep("xyz",10))
> > a
>    x   y   z
> 1   1 abc xyz
> 2   2 abc xyz
> 3   3 abc xyz
> 4   4 abc xyz
> 5   5 abc xyz
> 6   6 abc xyz
> 7   7 abc xyz
> 8   8 abc xyz
> 9   9 abc xyz
> 10 10 abc xyz
> > b=data.frame(x=a$x, y=a$y)
> > b
>    x   y
> 1   1 abc
> 2   2 abc
> 3   3 abc
> 4   4 abc
> 5   5 abc
> 6   6 abc
> 7   7 abc
> 8   8 abc
> 9   9 abc
> 10 10 abc
>
>
>
> Regards,
> Peng
>
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