Stacked tables vertically join columns from two or more other tables in the same document. Stacked tables are useful for combining data from multiple data sets with similar (though not necessarily identical) column layouts.
Creating a stacked table does not alter the component tables in any way. The contents of a stacked table are always computed on-the-fly, so changes to a component table will be instantly reflected in the stacked table (as well as its models and predictions).
Stacked tables have two additional columns called source_name and source_index; these columns contain the name of the table from which individual rows are taken, as well as the original row number.