[R] Summarize by two-column factor, retaining original factors

[Matt Crawford]

I am having trouble doing the following.  I have a data.frame like
this, where x and y are a variable that I want to do calculations on:

Name Year x y
ab   2001  15 3
ab   2001  10 2
ab   2002  12 8
ab   2003  7 10
dv   2002  10 15
dv   2002  3 2
dv   2003  1 15

Before I do all the other things I need to do with this data, I need
to summarize or collapse the data by name and year.  I've found that I
can do things like
nameyear<-interaction(name,year)
dataframe$nameyear<-nameyear
tapply(dataframe$x,dataframe$nameyear,sum)
tapply(dataframe$y,dataframe$nameyear,sum)
and then bind those together.

But my problem is that I need to somehow retain the original Names in
my collapsed dataset, so that later I can do analyses with the Name
factors.  All I can think of is something like
tapply(dataframe$Name,dataframe$nameyear, somefunction?)
but nothing seems to work.

I'm actually trying to convert a SAS program, and I can't get out of
that mindset.  There, it's a simple Proc Means, By Name Year.

Thanks for any help or suggestions on the right way to go about this.

Matt Crawford