[R] Calculating the mean of values in tables using formulae
Mark Alen
linux_jvm at yahoo.com
Sat Jul 23 07:02:10 CEST 2011
I know commands like xtabs and table allow a user to do cross-tabulation
For example the following command generates a pivot table that shows the number of cars that have the same number of gears and cylinders.
>xtabs(~cyl+gear,data =mtcars)
gear
cyl 3 4 5
4 1 8 2
6 2 4 1
812 0 2
>
We can extend the formula so it could show the sum of the horse power for the cars in each bin
>xtabs(hp~cyl+gear,data =mtcars)
gear
cyl 3 4 5
4 97 608 204
6 215 466 175
82330 0 599
>
I am now wondering, is it possible to calculate the mean of horse powers for cars in each bin? for example something like this xtabs(mean(hp)~cyl+gear, data = mtcars)
Thank you
Mark
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