Function for out of sample testing a linear model

Question

Can anyone recommend a function in R to me with which i can calculate the Out of Sample R-squared of a previously calculated linear model lm(). Regards and thanks in advance!

Answer 1

You could use the following format:

# Fit model 
model.lm <- lm(Sepal.Length ~ Petal.Length, data = iris[1:75,]) 

# Predict data for some new data 
pred.dat <- predict(model.lm, newdata = iris[76:150,]) 

# Calculate correlation between predicted values for new data and actual values, then square 
cor(iris[1:75,"Sepal.Length"], pred.dat)^2 

You can pack it all in a function if you like. If you need any help, just ask.

Cheers

Felipe