Using LINQ to group a list of strings based on known substrings that they will contain

Question

I have a known list of strings like the following:

List groupNames = new List(){\"Group1\",\"Group2\",\"Group3\"};

Answer 1

That looks like:

var query = from groupName in groupNames
            from data in dataList
            where data.StartsWith(groupName)
            group data by groupName;

Note that this isn't a join, as potentially there are overlapping group names "G" and "Gr" for example, so an item could match multiple group names. If you could extract a group name from each item (e.g. by taking everything before the first dot) then you could use "join ... into" to get a group join. Anyway...

Then:

foreach (var result in query)
{
    Console.WriteLine("Key: {0}", result.Key);
    foreach (var item in result)
    {
        Console.WriteLine("  " + item);
    }
}

If you really need the anonymous type, you can do...

var query = from groupName in groupNames
            from data in dataList
            where data.StartsWith(groupName)
            group data by groupName into g
            select new { g.Key, DataList = g.ToList() };