[R] Successive subsets from a vector?

[Atte Tenkanen]

Thanks!

I have used tons of for- and while-loops (I'm ashamed to reveal these scripts, but I'm primarily a musician;-) http://users.utu.fi/attenka/SetTheoryScripts.r), taken some or more cup of cocoa and mostly been happy ;-) Now I got so many new ways to do these things, that it takes a while to ruminate all the ideas here.

Atte

>    embed(VECTOR, 5)[, 5:1]
> 
> gives the subsets, so something like
> 
>    apply(embed(VECTOR, 5)[, 5:1], 1, paste, collapse="")
> 
> does the job.
> 
> The following is a bit more efficient
> 
>    ind <- 1:(length(VECTOR)-4)
>    do.call(paste, c(lapply(0:4, function(j) VECTOR[ind+j]), sep=""))
> 
> but by looking at how embed() works it could be made as efficient.
> 
> Larger example:
> 
> VECTOR <- sample(1:10, 1e5, replace=TRUE)
> > system.time(apply(embed(VECTOR, 5)[, 5:1], 1, paste, collapse=""))
> [1] 5.73 0.05 5.81   NA   NA
> > system.time({ind <- 1:(length(VECTOR)-4)
> + do.call(paste, c(lapply(0:4, function(j) VECTOR[ind+j]), sep=""))
> + })
> [1] 1.00 0.01 1.01   NA   NA
> 
> The loop method took 195 secs.  Just assigning to an answer of the 
> correct 
> length reduced this to 5 secs.  e.g. use
> 
>    ADDRESSES <- character(length(VECTOR)-4)
> 
> Moral: don't grow vectors repeatedly.
> 
> On Tue, 22 Aug 2006, kone wrote:
> 
> > I'd like to pick every imbricated five character long subsets 
> from a 
> > vector. I guess there is some efficient way to do this without 
> loops...> Here is a for-loop-version and a model for output:
> > 
> > VECTOR=c(1,4,2,6,5,0,11,10,4,3,6,8,6);
> > 
> > ADDRESSES=c();
> 
> You do not need the semicolons, and they just confuse readers.
> 
> > for(i in 1:(length(VECTOR)-4)){
> > 	ADDRESSES[i]=paste(VECTOR[i:(i+4)],collapse="")	
> > }
> > 
> >  > ADDRESSES
> > [1] "14265"   "42650"   "265011"  "6501110" "5011104" "0111043" 
> > "1110436" "104368"
> > [9] "43686"
> > 
> > 
> > Atte Tenkanen
> > University of Turku, Finland
> > 
> > 	[[alternative text/enriched version deleted]]
> > 
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> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
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