[R] Extracting clusters from Data Frame

[Gustaf Rydevik]

On Dec 10, 2007 2:28 PM, Johannes Graumann <johannes_graumann at web.de> wrote:
> Hello,
>
> I have a large data frame (1006222 rows), which I subject to a crude
> clustering attempt that results in a vector stating whether the datapoint
> represented by a row belongs to a cluster or not. Conceptually this looks
> something like this:
> Value   Cluster?
> 0.01    FALSE
> 0.03    TRUE
> 0.04    TRUE
> 0.05    TRUE
> 0.07    FALSE
> ...
> What I'm looking for is an efficient strategy to extract all consecutive
> rows associated with "TRUE" as a single cluster (data.frame
> representation?) without cluttering memory with thousends of data.frames.
> I was thinking of an independent data.frame that would contain a column of
> lists that reference all indexes from the big one which are contained in
> one cluster ...
> Can anyone kindly nudge me and let me know how to deal with this
> efficiently?
>
> Joh
>

How about :
orig.data<-sample(c(TRUE,FALSE),100,replace=T)
Cluster<-data.frame(c.ndx=cumsum(rle(orig.data)$lengths),c.size=rle(orig.data)$lengths,c.type=rle(orig.data)$values)
Cluster<-Cluster[Cluster$c.type==TRUE,]

##Then, to get all original data belonging to cluster three:
orig.data[rev(Cluster[3,"c.ndx"]-seq(length.out=Cluster[3,"c.size"])+1)]


Not the neatest solution, but I'm sure someone here can improve on it.
/Gustaf

-- 
Gustaf Rydevik, M.Sci.
tel: +46(0)703 051 451
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skype:gustaf_rydevik