[R] Count unique rows/columns in a matrix

[Gabor Csardi]

Chuck, thanks a lot, this is a very good starting point.

G.

On Sat, Jan 12, 2008 at 01:08:11PM -0800, Charles C. Berry wrote:
[...]
> Gabor,
> 
> Try this. Order the matrix rows, conpare adjacent rows, and run length 
> encode the logical vector of comparisons. Decode the rle() result to get 
> the counts, use the logical vector comparing adjacent rows to identify the 
> unique rows, and cbind() them together. Like this:
> 
> count.rows <-
>   function(x)
>   {
>     order.x <- do.call(order,as.data.frame(x))
>     equal.to.previous <-
>       rowSums(x[tail(order.x,-1),] != x[head(order.x,-1),])==0
>     tf.runs <- rle(equal.to.previous)
>     counts <- c(1,
>                 unlist(mapply( function(x,y) if (y) x+1 else (rep(1,x)),
>                               tf.runs$length, tf.runs$value )))
>     counts <- counts[ c(diff(counts) <= 0, TRUE ) ]
>     unique.rows <- which( c(TRUE, !equal.to.previous ) )
>     cbind( counts, x[order.x[ unique.rows ], ,drop=F] )
>   }
> 
> HTH,
> 
> Chuck
> 
[...]

-- 
Csardi Gabor <csardi at rmki.kfki.hu>    UNIL DGM