LINQ練習題 - 兩個集合做Union並且做Group彙總

先定義一下型別

public class SomeStatistics

{

public DateTime Day { get; set; }

public int Correct { get; set; }

public int Incorrect { get; set; }

}

然後有兩個此型別的集合

List<SomeStatistics> list1 = new List<SomeStatistics>();

list1.Add(new SomeStatistics() { Day = new DateTime(2010, 8, 1), Correct = 10, Incorrect = 2 });

list1.Add(new SomeStatistics() { Day = new DateTime(2010, 8, 2), Correct = 5, Incorrect = 3 });

list1.Add(new SomeStatistics() { Day = new DateTime(2010, 8, 3), Correct = 2, Incorrect = 4 });

list1.Add(new SomeStatistics() { Day = new DateTime(2010, 8, 4), Correct = 1, Incorrect = 5 });

List<SomeStatistics> list2 = new List<SomeStatistics>();

list2.Add(new SomeStatistics() { Day = new DateTime(2010, 7, 28), Correct = 10, Incorrect = 2 });

list2.Add(new SomeStatistics() { Day = new DateTime(2010, 7, 29), Correct = 11, Incorrect = 3 });

list2.Add(new SomeStatistics() { Day = new DateTime(2010, 7, 30), Correct = 12, Incorrect = 4 });

list2.Add(new SomeStatistics() { Day = new DateTime(2010, 7, 31), Correct = 13, Incorrect = 5 });

list2.Add(new SomeStatistics() { Day = new DateTime(2010, 8, 4), Correct = 5, Incorrect = 10 });

兩個集合的Union是這樣



可以看到最後有兩筆資料的Day是相同的，需求是要將Day做Group然後Correct、Incorrect的兩項欄位要做彙總


作法一

List<SomeStatistics> list3 = new List<SomeStatistics>();

list3.AddRange(list1);

foreach (var item in list2)

{

if (!list3.Select(s=>s.Day).Contains(item.Day))

{

list3.Add(item);

}

else

{

var target = list3.Where(s => s.Day == item.Day).FirstOrDefault();

target.Correct += item.Correct;

target.Incorrect += item.Incorrect;

}

}

結果顯示




作法二

List<SomeStatistics> result = new List<SomeStatistics>();

foreach (var item in list1.Union(list2).GroupBy(s=>s.Day))

{

result.Add(new SomeStatistics() { 

Day = item.Key,

Correct = list1.Union(list2).Where(s => s.Day == item.Key).Select(s => s.Correct).Sum(),

Incorrect = list1.Union(list2).Where(s => s.Day == item.Key).Select(s => s.Incorrect).Sum()

});

}

結果顯示




第一個方法是比較制式的，而第二個作法就有用到GroupBy與Sum方法

只是個練習題，但我想應該還有更加精簡而有效率的方法吧！？

希望能有朋友可以不吝指教更好的方法

謝謝

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