Is this what you mean?

z[which(z[,"x"] == 5) - 1, "y"]

?which is probably what you're looking for...

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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