[R] lm: how to calculate rsquared of the predicted values?

[Max Kuhn]

>
> 1.  can I measure de R-squared value between the predicted(by the model) and
> real (observed) values.?
> 2. Measure the RMSE error .
>

There is a function in the caret package called postResample that will
do that (even if you aren't using resampling).

As has been previously noted on this list, there are a number of
formulas for R-squared. This function uses the square of the
correlation between the observed and predicted. The next version of
caret will offer a choice of formulas.

-- 

Max