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
純粹是在寫興趣的，用寫程式、寫文章來抒解工作壓力