[R] subtotal, submean, aggregate

From: Patrick Giraudoux <patrick.giraudoux_at_univ-fcomte.fr>
Date: Mon 27 Feb 2006 - 00:24:19 EST


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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