[R] Tagging identical rows of a matrix

[Liaw, Andy]

Here's one possibility:

> index <- as.numeric(factor(apply(mat, 1, paste, collapse=":")))
> index
[1] 1 2 1 1 2 3


There's probably some better way though...

Andy

> From: Scott Waichler
> 
> I would like to generate a vector having the same length
> as the number of rows in a matrix.  The vector should contain
> an integer indicating the "group" of the row, where identical
> matrix rows are in a group, and a unique row has a unique integer.
> Thus, for
> 
> a <- c(1,2)
> b <- c(1,3)
> c <- c(1,2)
> d <- c(1,2)
> e <- c(1,3)
> f <- c(2,1)
> mat <- rbind(a,b,c,d,e,f)
> 
> I would like to get the vector c(1,2,1,1,2,3).  I know dist() gives
> part of the answer, but I can't figure out how to use it for
> this purpose without doing a lot of looping.  I need to apply this
> to matrices up to ~100000 rows.
> 
> Thanks,
> Scott Waichler
> Pacific Northwest National Laboratory
> scott.waichler_at_pnl.gov
> 
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