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. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.