On Sun, 26 Feb 2006, Patrick Giraudoux wrote:
> Dear All,
>
> I would like to make partial sums (or means or any other function) of
> the values in intervals along a sequence (spatial transect) where groups
> are defined.
>
> For instance:
>
> habitats<-rep(c("meadow","forest","meadow","pasture"),c(10,5,12,6))
> observations<-rpois(length(habitats),2)
> transect<-data.frame(observations=observations,habitats=habitats)
>
> aggregate() is not suitable for my purpose because I want a result
> respecting the order of the habitats encountered although they may have
> the same name (and not pooling each group on each level of the factor
> created). For instance, the output of the ideal function
> mynicefunction() would be something as:
>
> mynicefunction(transect$observations, by=list(transect$habitats),sum)
> meadow 16
> forest 9
> meadow 21
> pasture 17
>
> and not
>
> aggregate(transect$observations,by=list(transect$habitats),sum)
> Group.1 x
> 1 forest 9
> 2 meadow 37
> 3 pasture 17
>
> Did anybody hear about such a function already written in R? If no, any
> idea to make it simple and elegant to write?
I got as far as:
rle.habs <- rle(habitats)
habitats1 <- rep(make.names(rle.habs$values, unique=TRUE), rle.habs$lengths)
aggregate(observations,by=list(habitats1),sum)
making an extra habitats vector with a unique label for each run.
Since I don't know your seed, the results are not the same, but rle() is
quite good for runs.
Roger
>
> Cheers,
>
> Patrick Giraudoux
>
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [EMAIL PROTECTED]
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