On Dec 3, 2009, at 1:50 PM, Peng Cai wrote:
Hi R Users,
I'm wondering how can I calculate two (or three) way sum of a
variable. A
sample data is:
State Month Year Value
NC Jan 1996 1
NC Jan 1996 2
NC Feb 1997 2
NC Feb 1997 3
NC Mar 1998 3
NC Mar 1998 4
NY Jan 1996 4
NY Jan 1996 5
NY Feb 1997 5
NY Feb 1997 6
NY Mar 1998 6
NY Mar 1998 7
I'm trying to sum up "value" column by State*Month and by
State*Month*Year.
?tapply
as in
sum.tbl <- with(dftbl, tapply(Value, list(State, Month), sum) )
Also, I may need to calculate mean value along with "sum".
Use the mean function in the above formulation to get means, length to
get counts, or perhaps summary .... or one of the several packages
that offer a "describe" function. So many functions, so little time.
-- David
Any help would be greatly appreciated,
Thanks,
Peng
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and provide commented, minimal, self-contained, reproducible code.
