Lambda 计算 IEnumerable 中字符串的出现次数

Question

如何在单行 lambda 表达式中重写下面的 GetCounts() 方法？请注意，它必须是 lambda 表达式（不能是 LINQ）。我正在尝试做这样的事情，但无法弄清楚确切的语法：

return items.GroupBy(e => e).ToDictionary<string, int>(e => e,e => e.Count());

代码：

static void Main(string[] args)
{
    string[] colours = new string[] { "Blue", "Blue", "Green", "Red" };
    Dictionary<string, int> values = GetCounts(colours);

    foreach (KeyValuePair<string, int> v in values)
        Console.WriteLine($"{v.Key}:{v.Value}");

    //Desired output:
    //Blue:2
    //Green:1
    //Red:1
    Console.ReadKey();
}

public static Dictionary<string, int> GetCounts(IEnumerable<string> items)
{
    var counts = new Dictionary<string, int>();

    foreach (string item in items)
        counts[item] = !counts.ContainsKey(item) ? 1 : ++counts[item];

    return counts;
}

Answer 1

你需要分组的Key

即

items.GroupBy(e => e).ToDictionary(k => k.Key, v => v.Count());