Re: [R] linear regression "group by"

From: Michael Dewey <info_at_aghmed.fsnet.co.uk>
Date: Wed, 16 Apr 2008 17:52:15 +0100

At 18:03 14/04/2008, Ryan Lauritsen wrote:
>Hi all. I'm brand new to R.
>
>My dataset (stored in MySQL) is a list of weather stations in rows by
>year with various weather variables in columns, for example:
>STNID YEAR TEMP DEWP
>station1 1990 54 50
>station1 1991 23 10
>station1 1992 34 18
>station2 1990 45 41
>station2 1991 32 25
>station2 1992 21 11
>
>I'm trying to run linear regression and get the basic output (i.e.
>intercept, slope, and significance) for each station. I'm able to run
>the regression on the entire dataset using:
>lm(TEMP~DEWP, data=select)
>But is there a way to aggregate the data ("group by" in MySQL) by
>STNID during the regression? Ideally I would just have a list of
>stations and their approriate summary output, which I could use for
>further analysis.

In this particular case you might consider using lmList from the nlme package (or from lme4).

More generally you could look at the family of apply functions: apply, tapply, sapply, and so on.

>I've searched the manual, etc. for solutions, but have been
>unsuccessful. Any assistance is greatly appreciated.
>
>Thank you,
>Ryan

Michael Dewey
http://www.aghmed.fsnet.co.uk



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