[R] Data Manipulations - Group By equivalent

[Frank E Harrell Jr]

zubin wrote:
> Hello, a beginner R user - boy i wish there was a book on just data 
> manipulations for SAS users learning R (equivalent to the SAS DATA 
> STEP)..  Okay, my question: 
> 
> I have a panel data set, hotel data occupancy by month for 12 months, 
> 1000 hotels.  I have a field labeled 'year' and want to consolidate the 
> monthly records using an average into 1000 occupancy numbers - just a 
> simple average of the 12 months by hotel.  In SQL this operation is 
> pretty easy, a group by query (group by hotel where year = 2005, avg 
> occupancy) - how is this done in R? (in R language not SQL).  Thx!
> 
> -zubin
> 
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This is in the most basic R documentation.  Please read it.

-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University