C# 获取 List 中不同值的列表
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Get a list of distinct values in List
提问by Darrel Hoffman
In C#, say I have a class called Note with three String member variables.
在 C# 中，假设我有一个名为 Note 的类，其中包含三个 String 成员变量。
public class Note
{
public string Title;
public string Author;
public string Text;
}
And I have a list of type Note:
我有一个注意类型的列表：
List<Note> Notes = new List<Note>();
What would be the cleanest way to get a list of all distinct values in the Author column?
在 Author 列中获取所有不同值的列表的最简洁方法是什么？
I could iterate through the list and add all values that aren't duplicates to another list of strings, but this seems dirty and inefficient. I have a feeling there's some magical Linq construction that'll do this in one line, but I haven't been able to come up with anything.
我可以遍历列表并将所有不重复的值添加到另一个字符串列表中，但这看起来很脏而且效率低下。我有一种感觉，有一些神奇的 Linq 结构可以在一行中做到这一点，但我一直想不出任何东西。
采纳答案by Kirk Woll
Notes.Select(x => x.Author).Distinct();
This will return a sequence (IEnumerable<string>) of Authorvalues -- one per unique value.
这将返回一个值序列 ( IEnumerable<string>) Author—— 每个唯一值一个。
回答by Dan Busha
Jon Skeet has written a library called morelinqwhich has a DistinctBy()operator. See herefor the implementation. Your code would look like
Jon Skeet 编写了一个名为morelinq的库，它有一个DistinctBy()运算符。见这里的实现。你的代码看起来像
IEnumerable<Note> distinctNotes = Notes.DistinctBy(note => note.Author);
Update:After re-reading your question, Kirk has the correct answer if you're just looking for a distinct set of Authors.
更新：在重新阅读您的问题后，如果您只是在寻找一组不同的作者，柯克就会得到正确的答案。
Added sample, several fields in DistinctBy:
添加了示例，DistinctBy 中的几个字段：
res = res.DistinctBy(i => i.Name).DistinctBy(i => i.ProductId).ToList();
回答by ravinderreddy Seeelam
mcilist = (from mci in mcilist select mci).Distinct().ToList();
回答by atik sarker
Distinct the Note class by Author
按作者区分 Note 类
var DistinctItems = Note.GroupBy(x => x.Author).Select(y => y.First());
foreach(var item in DistinctItems)
{
//Add to other List
}
回答by Bhaskar
public class KeyNote
{
public long KeyNoteId { get; set; }
public long CourseId { get; set; }
public string CourseName { get; set; }
public string Note { get; set; }
public DateTime CreatedDate { get; set; }
}
public List<KeyNote> KeyNotes { get; set; }
public List<RefCourse> GetCourses { get; set; }
List<RefCourse> courses = KeyNotes.Select(x => new RefCourse { CourseId = x.CourseId, Name = x.CourseName }).Distinct().ToList();
By using the above logic, we can get the unique Courses.
通过上面的逻辑，我们可以得到唯一的Courses。
