A very handy feature to use with Collections is the Compare and Combine view, which allows you to see items that selected Collections have in common and then to see the items from those Collections together in one view. This is especially helpful for eliminating duplicate items.

To compare the contents of two or more Collections, click to open the first Collection and then Shift-Click on the second. (Shift-Option for Mac users.) If there are items in common, they will be displayed in the Edit window. A Venn diagram symbol showing overlapping circles will appear in the top left corner of the Edit window.

To combine the contents of these Collections, click on the symbol and all of the contents of the selected Collections will be displayed in the Edit window together. The symbol will change to reflect two adjoining circles. Click once again to return to the compare view.