[R] Error in model.frame

[Uwe Ligges]

Göran Broström wrote:
> 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