Hi there,
  I´m a newbie in R and I´m looking for some advice how to teste Piecewise (Broken Stick) models. 
   
  I´have another simple question: how can I compute descriptive statistics for data grouped for two or more variables? See below, please.
   
  Year  Site Repetition rainfall
   1980  1         1         ...
   1980  1         2         ...
   1980  1         3         ...
   1980  2         1         ...
   1980  2         2         ...
   1980  2         3         ...
   
   1990  1         1         ...
   1990  1         2         ...
   1990  1         3         ...
   1990  2         1         ...
   1990  2         2         ...
   1990  2         3         ...
   
  I´d like to compute the mean rainfall for each YEAR * SITE combination.
   
  Kind regards,
   
  Miltinho

		
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