I would like to ask how to use MATLAB to append new columns into existing excel file without altering the original data in the file? In my case I don't know the original number of columns and rows in the file and it is inefficient to open the files one by one and check in practice. Another difficulty is that the new columns may have different number of rows to the existing data so that I cannot use the trick of reading in the data, forming a new matrix and replace the data with the new matrix. I have seen many posts teaching people how to add new rows but adding new column seems quite a different thing since the columns are named by letters instead of numbers. Thank you.