new: unqiue keyword for add_virtual_columns to make sure the column name is not overwritten
new: unqiue keyword for add_virtual_columns to make sure the column name is not overwritten

maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex