[R] subtotal, submean, aggregate

[Gabor Grothendieck]

Create another variable that gives the run number and aggregate on
both the habitat and run number removing the run number after
aggregating:

runno <- cumsum(c(TRUE, diff(as.numeric(transect[,2])) !=0))
aggregate(transect[,1], list(obs = transect[,2], runno = runno), sum)[,-2]

This does not give the same as your example but I think there are some
errors in your example output.

On 2/26/06, Patrick Giraudoux <patrick.giraudoux at univ-fcomte.fr> 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?
>
> Cheers,
>
> Patrick Giraudoux
>
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