如何创建多个数据模型，然后选择被评估为最佳拟合的模型？

I have a training-test function set up in R that takes a set of data, excludes a certain portion of it (to preclude the model overfitting the data), and then trains a linear model on about half of the remaining data before testing the model on the other half. I have a training-test function set up in R tha