Looping through multiple files with multiple column names

Hello, I have a looping workflow to iterate over multiple files to get the names of the columns in each file. I am using a grouping node to obtain the number of unique values per column, but since column names vary my workflow stops once a file where none of the columns is matching any of the columns in the original file I used to test and configure the loop. My problem is that I don’t know how to configure this dynamically in the group node, i.e. how to feed the column names dynamically to the aggregation.

Help will be much appreciated.