I recently ran into the following:
x <- c(1,2,4,3) lm(x ~ 1:length(x))
Error in model.frame(formula, rownames, variables, varnames, extras, extranames, : variable lengths differ
but
lm(x ~ c(1:length(x)))
Call: lm(formula = x ~ c(1:length(x)))
Coefficients:
(Intercept) c(1:length(x)) 0.5 0.8
and
identical(1:4, c(1:4))
[1] TRUE
Should I report this as a bug?
NO!!! The ":" operator is used to model interactions in lm() and friends!
Use lm(x ~ I(1:length(x))) in order to perform the analysis above.
Uwe Ligges
Göran
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