[R] Simple use of dcast (reshape2 package)

[Patrick Connolly]

Suppose I have a small dataframe

> aa
     Target Eaten ID
50      TPP     0  1
51      TPP     1  2
52      TPP     3  3
53      TPP     1  4
54      TPP     2  5
50.1    GPA     9  1
51.1    GPA    11  2
52.1    GPA     8  3
53.1    GPA     8  4
54.1    GPA    10  5

And I want to reshape it into 

  ID TPP GPA
1  1   0   9
2  2   1  11
3  3   3   8
4  4   1   8
5  5   2  10

I realise that dcast function in the reshape2 package can handle much
more complicated tasks than that, but I can't make it do a simple one.

If I simply tried 

> dcast(aa, ... ~ Target)
Using ID as value column: use value.var to override.
Aggregation function missing: defaulting to length
  Eaten GPA TPP
1     0   0   1
2     1   0   2
3     2   0   1
4     3   0   1
5     8   2   0
6     9   1   0
7    10   1   0
8    11   1   0

As per the help file, it's giving counts of the numbers in the Eaten
column since that's the default fun.aggregate value.

My questions are: what fun.aggregate would work?  Alternatively, can
value.var be set to something useful?

TIA

-- 
~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.   
   ___    Patrick Connolly   
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 _( Y )_  	         Average minds discuss events 
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