Some time ago while developing a project I came across a problem related to Linq to Objects. I wanted do join a single object with a collection in order to transverse them with a foreach statement (the item was not allways present and I wanted to treat it as a regular element in the original collection).
Using the intellisense to find a Linq to Objects extension method that fitted my needs I didn’t find that particular functionality, but I thought about an alternative: creating a collection with the single element and joining the two collections with one of the two extension methods that seem promising to this new task: Union and Concat.
After reading the documentation and writing the example above I became aware of the difference. Union acts as a mathematical set operator, adding the elements of both lists into a single list without repeated elements. Contat, by the other hand keeps the repeated elements.
