Hi Gary,

Try

transform(z, y = ifelse(x == 5, y-1, y))

HTH,
Jorge

On Tue, Feb 22, 2011 at 12:18 PM, Hongwei Dong <> wrote:

> Hi, R users,
>
> I'm wondering if I can identify an element in a column by an element in
> another column. For example:
>
> x<-1:10
> y<-11:20
> z<-cbind(x,y)
> z
>     x  y
>  [1,]  1 11
>  [2,]  2 12
>  [3,]  3 13
>  [4,]  4 14
>  [5,]  5 15
>  [6,]  6 16
>  [7,]  7 17
>  [8,]  8 18
>  [9,]  9 19
> [10,] 10 20
>
> What I want to do is: when x=5, y=y-1
>
> Anyone can tell me how to do this? Thanks.
>
>
> Gary
>
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>
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