[R] Summarising by group

[peter dalgaard]

On May 9, 2011, at 11:12 , Martyn Byng wrote:

> I wonder if someone with more experience than me on using R to summarise
> by group wants to post a reply to this 

Not really (but how did those people manage to overlook by()?). However, another matter

PLEASE DO NOT BE SO B***DY LAZY AND START A NEW TOPIC AS A REPLY TO SOMETHING COMPLETELY UNRELATED. 

Those of us with threading mail clients, will see your post as part of the thread 

"maximum likelihood convergence reproducing Anderson Blundell 1982 Econometrica R vs Stata"

and, at least with Mac OSX's Mail, the header of the entire thread is now "Summarising by group".

Peter D.


> 
> http://www.analyticbridge.com/group/sasandstatisticalprogramming/forum/t
> opics/why-still-use-sas-with-a-lot
> 
> To save everyone having to follow the link, the text is copied below
> 
> "SAS has some nice features, such as the SQL procedure or simple "group
> by" features. Try to compute correlations "by group" in R: say you have
> 2,000 groups, 2 variables e.g. salary and education level, and 2 million
> observations - you want to compute correlation between salary and
> education within each group.
> 
> It is not obvious, your best bet is to use some R package (see sample
> code on Analyticbridge to do it), and the solution is painful, you can
> not return both correlation and stdev "by group", as the function can
> return only one argument, not a vector. So if you want to return not
> just two, but say 100 metrics, it becomes a nightmare."
> 
> 
> 
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-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com