Applying by function to lm()

Question

I am new to R and I am just learning about the apply functions and how they work. I simply want to extract the coefficients from a lm fit on a var

Answer 1

This is much easier in more modern packages, e.g. data.table:

library(data.table)
setDT(d)
d[ , .(reg = list(lm(x ~ color))), by = year]
#    year  reg
# 1: 2012 
# 2: 2006 
# 3: 2011 
# 4: 2008 
# 5: 2007 
# 6: 2010 
# 7: 2009 

The reg column has lm objects; note we need to wrap lm in list(.) so that data.table doesn't confuse the plain list (note that is.list(lm(x ~ color, data = d)) is TRUE.