[R] How to calculate the stratified means in a data frame?

[Frank Duan]

Got it. Many thanks.


On Thu, 18 Nov 2004 13:10:53 -0800, Jeff Laake <jeff.laake at noaa.gov> wrote:
> look at "by"
> 
> 
> 
> Frank Duan wrote:
> 
> > Dear R people,
> >
> > I have a simple question to ask. Suppose I have a data.frame with two
> > variables: one factor (x) and one numeric (y), I want to calculate the
> > mean of y for each value of x. Although it's easy to do it within a
> > for a loop, I believe there may be a concise way by using some kinds
> > of "apply" functions. Could anyone tell me how to do that? Thank you.
> >
> > Frank
> >
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