In my previous post about using the KeywordQuery class, I had one small omission. The fact is that when you add your own managed properties using the SelectProperties collection of the keyword class, the data type you get back is a string containing 1 element instead of a string. This can be quite annoying when you are attempting to do data binding as well as additional filtering. I have found this to really only be the case when dealing with custom managed properties. Default properties such as title and content source always return a string. To combat this use LINQ to read the data into a new anonymous type. You can then bind the data and filter as needed.
var results = from queryResult in queryDataTable.AsEnumerable()
Title = queryResult.Field<string>("ContentSource"),
Size = (queryResult.Field<string>("Size").Any()) ? queryResult.Field<string>("Size") : null
In the above example, I specify ContentSource as a string just like normal. However, for my custom manager property Size, I have to cast to a string and then I simply return the first element. Technically, I should probably check to make sure that the element exists as well (but I am checking for null). Once everything is copied into the anonymous type, you can bind, group, or filter it as needed.