The Cologne R user group met last Friday for two talks on split apply combine in R and XLConnect by Bernd Weiß and Günter Faes respectively, before the usual Schnitzel and Kölsch at the Lux.
Split apply combine in R The apply family of functions in R is incredible powerful, yet for newcomers often somewhat mysterious. Thus, Bernd gave an overview of the different apply functions and their cousins.

The ave function in R is one of those little helper function I feel I should be using more. Investigating its source code showed me another twist about R and the “[” function. But first let’s look at ave.
The top of ave’s help page reads:
Group Averages Over Level Combinations of Factors
Subsets of x[] are averaged, where each subset consist of those observations with the same factor levels.

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