With Data Mash Up, you could merge feeds in order to add new information or new items.
You can mash a feed with another feed/feed view (up to 5 different sources).
Open the feed/feed view you wish to add to, and click +Data Mashup > +Data Source > Data Feed:
Possible merge types:
1. Side by side: This option will be used to add more information about products, that is split between 2 different feeds. There needs to be a common, unique value in both feeds for us to use as reference for the merge (primary key – ID for example).
Additional columns will be added to the feed you are working on. To select more than one additional column, use the Ctrl key when selecting.
Select the feed you wish to merge.
Set your Primary Key (usually the ID column) and the columns that you wish to merge from the external feed. Select Multiple column by pressing on the Ctrl.
2. Rows: The feeds should have the same structure (identical columns) in order to add new products.
Select the feed you wish to import the new items from: