Hi Luc,
First of all, questions like this should really be asked on the R-help
mailing list.
The tapply function does what you want:
> year
[1] 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2
Levels: 1 2
> area
[1] a a a a a b b b b a a a a b b b b b
Levels: a b
> value
[1] 20 25 28 31 23 25 28 23 19 25 23 24 26 27 28 20 25 28
Note that both year and area are factors.
Get the mean for each area:
> tapply(value, area, mean)
a b
25.00000 24.77778
If you make the second argument a list then you can subset on both
factor columns:
> tapply(value, list(year, area), mean)
a b
1 25.4 23.75
2 24.5 25.60
Kjell
On 4 sept. 08, at 09:06, RFTW wrote:
Hi all
I have a very basic question, yet i have not found how to do it.
Suppose my dataset looks like this:
Year Area value
1 a 20
1 a 25
1 a 28
1 a 31
1 a 23
1 b 25
1 b 28
1 b 23
1 b 19
2 a 25
2 a 23
2 a 24
2 a 26
2 b 27
2 b 28
2 b 20
2 b 25
2 b 28
Now, i want to calculate a MEAN per year per area. How do i do that?
With mean(value) i calculate the mean of all values of course. I
just need
to know how to group year and area correctly.
I assume that i can use this grouping in other calculations too,
right?
Cheers,
Luc
--
View this message in context:
http://www.nabble.com/calculating-means-per-group-tp19271479p19271479.html
Sent from the R devel mailing list archive at Nabble.com.
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
