[R] mean for subset

[Gabor Grothendieck]

Have a look at this post and the rest of that thread:

https://stat.ethz.ch/pipermail/r-help/2010-January/223420.html

On Tue, Jan 5, 2010 at 1:29 PM, Geoffrey Smith <gps at asu.edu> wrote:
> Hello, does anyone know how to take the mean for a subset of observations?
> For example, suppose my data looks like this:
>
> OBS     NAME   SCORE
> 1          Tom       92
> 2          Tom       88
> 3          Tom       56
> 4          James    85
> 5          James    75
> 6          James    32
> 7          Dawn     56
> 8          Dawn     91
> 9          Clara     95
> 10        Clara     84
>
> Is there a way to get the mean of the SCORE variable by NAME but only when
> the number of observations is equal to 3?  In other words, is there a way to
> get the mean of the SCORE variable for Tom and James, but not for Dawn and
> Clara?  Thank you.
>
> --
> Geoffrey Smith
> Visiting Assistant Professor
> Department of Finance
> W. P. Carey School of Business
> Arizona State University
>
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>
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