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One possible method to group using the outcome of an asynchronous Task<string> and receive a grouping by string in C# is as follows:

1. Define a list of Task<string> objects to represent the asynchronous operations that generate strings, e.g.:

List<Task<string>> tasks = new List<Task<string>>()
{
    GetStringAsync("foo"),
    GetStringAsync("bar"),
    GetStringAsync("baz"),
};

1. Use the Task.WhenAll method to wait for all the tasks to complete asynchronously, and then extract the results using the Task.Result property, e.g.:

Task<string>[] results = await Task.WhenAll(tasks);

1. Use LINQ's GroupBy method to group the results by the first character of each string, e.g.:

var groups = results.GroupBy(s => s[0]);

1. Iterate over the groups and print out the key and the count of items in each group, e.g.:

foreach (var group in groups)
{
    Console.WriteLine("{0}: {1}", group.Key, group.Count());
}

This will produce output like the following:

f: 1
b: 2