Summarising headers of a table

I am looking to summarise a table, basically, imagine a table with names of products along the top horizontal header row and the name of the months along the vertical column side of the table. For each product in the body of the table there is the number of products sold per month for each product. A lot of products have blank cells in the body as they weren't sold that month. I would like to summarise per month, which products were sold (not the detail in the body of the table as the number of times it was sold is irrelevant). So to be able to show a list or new table showing that in January we sold x,y and z products (ignoring what is in the body of the table just picking up which headers have contents greater than zero per month by row) Thanks!