.net - Simple LINQ question in C#

Question

I am trying to use LINQ to return the an element which occurs maximum number of times AND the number of times it occurs.

For example: I have an array of strings:

string[] words = { "cherry", "apple", "blueberry", "cherry", "cherry", "blueberry" };

//...
Some LINQ statement here
//...

In this array, the query would return cherry as the maximum occurred element, and 3 as the number of times it occurred. I would also be willing to split them into two queries if that is necessary (i.e., first query to get the cherry, and second to return the count of 3.

Answer 1

The solutions presented so far are O(n log n). Here's an O(n) solution:

var max = words.GroupBy(w => w)
               .Select(g => new { Word = g.Key, Count = g.Count() })
               .MaxBy(g => g.Count);
Console.WriteLine(
    "The most frequent word is {0}, and its frequency is {1}.",
    max.Word,
    max.Count
);

This needs a definition of MaxBy. Here is one:

public static TSource MaxBy<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, IComparable> projectionToComparable
) {
    using (var e = source.GetEnumerator()) {
        if (!e.MoveNext()) {
            throw new InvalidOperationException("Sequence is empty.");
        }
        TSource max = e.Current;
        IComparable maxProjection = projectionToComparable(e.Current);
        while (e.MoveNext()) {
            IComparable currentProjection = projectionToComparable(e.Current);
            if (currentProjection.CompareTo(maxProjection) > 0) {
                max = e.Current;
                maxProjection = currentProjection;
            }
        }
        return max;                
    }
}