Summarize by two or more attributes

Marc, 
 How could I also apply the spline function to each of the 'columns' found in the result   from 

tapply(Df$Rate,list(Df$Bin,Df$Type),sum)

??

Something along the lines of the following:

  apply(tapply(Df$Rate,list(Df$Bin,Df$Type),sum), 2, spline)


If I am understanding what you want to do. 

Depending upon what you are trying to do, you may want to look at the other functions listed in the See Also in ?spline.

HTH,

Marc