c# - C# 中的简单 LINQ 问题

Question

我正在尝试使用 LINQ 返回出现最大次数的元素及其出现的次数。

例如:我有一个字符串数组:

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

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

在此数组中，查询将返回 cherry 作为最大出现元素，3 作为它出现的次数。如果有必要，我也愿意将它们分成两个查询(即，第一个查询获取 cherry，第二个查询返回 3 的计数。

Answer 1

目前给出的解决方案是O(n log n)。这是一个 O(n) 解决方案:

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
);

这需要 MaxBy 的定义。这是一个:

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;                
    }
}