[R] counting run lengths

[Richard.Cotton at hsl.gov.uk]

> >> It works, but the for (i in ...) loop slows down the simulation a 
lot.
> >>
> >> Any suggestion on how to avoid this loop? (or in general, to speed up 

> >> this part of the simulation)

> Actually, I have not  specified the following:  i want to consider only
> the "most recent" sequence of zeros, that is the last part of the time
> series.
> 
> That is, If  I have:
> 
>     [,1] [,2] [,3] [,4]
> [1,]    0    1    0    1
> [2,]    1    1    1    1
> [3,]    1    1    0    1
> [4,]    1    1    0    1
> [5,]    1    1    0    1
> [6,]    0    1    0    1
> [7,]    0    1    0    1
> [8,]    0    1    0    1
> [9,]    0    1    0    1
> 
> I want to store the values (4 0 7 0) in unSpells. That is the values
> that represent the "last" sequence of zeros (that is I want to ignore
> other possible zeros like the ones I have inserted above).

This runs pretty quickly:
unSpells <- nrow(Atr) - apply(Atr,2,function(x) max(which(x==1))) 
#c(4,0,7,0)

Regards,
Richie.

Mathematical Sciences Unit
HSL


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