TWSE | Taiwan Stock Exchange API | REST library

Here is a demo that may be helpful for you.

You can upload a .csv file to the shiny app. It will ignore the first column (or you can modify to specifically remove a date column).

The numeric inputs will be dynamically generated based on the header column names read in.

The demo has a calc button, that will store the input data and for further processing (calculating returns). Also added a table to show the entered data.

Edit: If upon pressing the calc button you want to call your custom function (calculate_portfolio_returns), you can add the call to that function in eventReactive, since that is dependent on the input button. To pass on the values from the numeric inputs, you can store these values temporarily in a vector vals, and then pass vals as an argument to the function (see modified code below). In the demo, I call a custom function calc_sum that will print the sum of the numeric inputs in the console. One final note, I added an explicit return at the end of input_vals(), so that vals can be shared for use in output$table.