[R] replacing duplicate rows

Peter Ehlers ehlers at ucalgary.ca
Thu Jul 21 22:06:21 CEST 2011

On 2011-07-21 09:59, cassie jones wrote:
> Hi all,
> I have a matrix which looks like the following,
> x=matrix(c(1,2,3,4,3,5,4,6,4,9),5,2,byrow=T)
> Now, I want to replace the 2nd columns of those 4 rows which have duplicate
> entries in the 1st column. For example, x[2,1]=x[3,1]=3 and I want to
> replace x[3,2] by x[2,2]. Similarly, I want to replace x[5,2] with x[4,2],
> which means that for duplicate entries in the 1st column, I want to replace
> the corresponding entries in the 2nd column with its 1st entry of the
> duplicate row.

Try match():

  idx <- match(x[,1], x[,1])
  x[,2] <- x[idx,2]

Peter Ehlers

> Can anybody help me in this regard?
> Thanks,
> Cassie
> 	[[alternative HTML version deleted]]
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