Suppose I have a list of time cards from multiple employees, but I want to group them into dictionary, based on the Social Security Number (SSN) of the employee. Here is an example of how to convert a list of items into a dictionary of lists:
Dictionary<string, List<TimeCardInfo>> dict;
dict = ( from timecard in listOfTimeCards
group timecard by timecard.SSN ).ToDictionary( x => x.Key, x => x.ToList() );