I use mostly <b>withFilter</b> whenever I can for single traversal usage. The <b>filter</b> method creates a new filtered collection in place while <b>withFilter</b> is a view that wraps the filtered collection and that is applied lazily as you traverse the collection (here triggered by <b>map</b>). This is great for very large collection but probably not very useful here. I did it more out of habit than anything else.