Hello.  The data.table package is very helpful in terms of speed.  But I am
having trouble actually using the output from linear regression.  Is there
any way to get the data.table output to be as pretty/useful as that from
the plyr package?  Below is an example.

library('data.table');
library('plyr');

REG <- data.table(ID=c(rep('Frank',5),rep('Tony',5),rep('Ed',5)),
y=rnorm(15), x=rnorm(15), z=rnorm(15));
REG;

#The ddply function from the plyr package produces very neat and useful
output;
ddply(REG, .(ID), function(x) coef(lm(y ~ x + z, data=x)));

#The data.table output is fast, but not very neat (in terms of the order of
the coefficient estimates).  Is there any way to get the data.table output
to look more like the plyr/ddply output (without making a list for each
coef and running the regression two times)?
REG[, coef(lm(y ~ x + z)), by=ID];

Thank you!  Geoff

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