r插入符号估计适合于完整数据的子集的参数

I have a dataset of 550k items that I split 500k for training and 50k for testing. During the training stage it is necessary to establish the 'best' combination of each algorithms' parameter values. Rather than use the entire 500k for this I'd be happy to use a subset, BUT when it comes to training the final model, with the 'best' combination, I'd like to use the full 500k. In pseudo code the task looks like:I have a dataset of 550k items that I split 500