如何从函数中的循环中添加数据框？

I have a function whose purpose is to predict revenue from cost. The twist is, I have as inputs many different dataframes, and many different corresponding models to predict with - the function loops through each dataframe, predicting on it its corresponding model and outputing a prediction output with confidence intervals. Now, I need to find a way to add all of these prediction outputs up. I have a function whose purpose is to predict r