Hi elh,

You could try using split() and lapply() instead (untested):

mymodels <- lapply(split(usage, ActNo),
function(l) lm(AvgKWh ~ AvgHDD + AvgCDD, data = l)
 )
To access the coefficients for all models you can do

lapply(mymodels, coef)

and, to access model number one (first ActNo),

mymodels[[1]]
summary(mymodels[[1]])

See ?split and ?lapply for more information.

HTH,
Jorge


On Wed, Aug 24, 2011 at 1:51 PM, elh <> wrote:

> Apologies for the elementary nature of the question (yes, I'm another
> newbie)...
>
> I'd like to perform a multiple regression on a single data set containing a
> representation of energy consumption and temperatures containing account
> number, usage (KWh), heating degree days (HDD) and cooling degree (CDD)
> days.  I want to get the coefficients back from the following equation:
>    lm(AvgKWh ~ AvgHDD + AvgCDD, data=usage)
>
> Given that the data set contains the usage of different accounts (e.g. some
> large energy users and some small energy users) I do not want to perform
> the
> equation just one time.  Instead, I want to re-calculate the coefficients
> (and associated measures of goodness of fit) for each account using the
> same
> equation and return the corresponding coefficients by the account number
> identifier.
>
> I thought I had figured out how to do this using  "by" and "sapply" formula
> but I keep getting an error message of: "$ operator is invalid for atomic
> vectors"
>
> Here is what I've bee trying to use
> # data is stored in a table called "usage"; other than the "ActNo" field,
> all the fields are numeric
> byDD <- function(data) {lm(AvgKWh~ AvgHDD + AvgCDD, data=data)}
> byActNo <- by(usage, usage$ActNo, FUN=byDD)
> sapply(byActNo, summary(byActno)$coef)
>
> Thanks in advance!  I'm sure a similar question has been covered somewhere
> but everytime I follow the message stream I hit a deadend.
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/Regression-by-factor-using-sapply-tp3766145p3766145.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
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> PLEASE do read the posting guide
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>

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