序言

Question

我正在MVC中编写一个LinQ查询，根据他们的分数返回学生的等级

// Merge the LB lists to get aggregated List, allot dummy rank(0)
var a = leaderboard.ToDictionary((kvp => kvp.Key),
(kvp => kvp.Value.leaderboard)).Values.SelectMany(x => x).GroupBy(student => student.stId).Select(
g => new Leaderboard { 
stId = g.Key, 
stName = g.Select(x => x.stName).First(), 
rank = 0, 
score = g.Select(x => x.score).Sum(), 
cName = g.Select(x => x.cName).First() 
});

// Arrange the records in descending order of scores for rank
lbList = a.ToList().OrderByDescending(q => q.score).ToList();
int rank = 1;
lbList = lbList.Select(c => { c.rank = rank++; return c; }).ToList();

但是对于相同的分数，这会返回不同的等级。看作分数是唯一没有时间分量的参数，如何更改此分数以返回相同分数的相同排名？

Answer 1

按顺序创建一个独特的分数集合，然后使用该集合中当前学生分数的位置作为他的排名：

var UniqueScores = a.OrderByDescending(x=>x.score).Select(x=>x.score).Distinct().ToArray;
lbList = lbList.Select(c => { c.rank = (UniqueScores.IndexOf(c.score) + 1); return c; }).ToList();

Answer 2

序言

这段代码看起来很可疑：

var a = leaderboard.ToDictionary((kvp => kvp.Key),
(kvp => kvp.Value.leaderboard)).Values.SelectMany(x => x).GroupBy(student => student.stId).Select(
g => new Leaderboard { 
stId = g.Key, 
stName = g.Select(x => x.stName).First(), 
rank = 0, 
score = g.Select(x => x.score).Sum(), 
cName = g.Select(x => x.cName).First() 
});

SelectMany(x => x)。这有什么意义？它什么也没做。
g.Select(x => x.cName).First()。它不是最优的，也不是可读的：g.First().cName。
ToDictionary ...再次，在您的案例中没有任何操作，因为您最终只使用Values。

所以，我会像这样重写它：

var a = leaderboard.
    Select(x => x.Value.leaderboard).
    GroupBy(student => student.stId).
    Select(
        g => new Leaderboard { 
            stId = g.Key, 
            stName = g.First().stName,
            rank = 0, 
            score = g.Sum(x => x.score),
            cName = g.First().cName});

排序

有一点需要考虑。您的代码以ToList()结尾。如果你想将List<>作为输出，那么简单的for循环是我认为最好的解决方案：

var lbList = a.OrderByDescending(x => x.score);
int rank = 1;
for (int i = 0; i < lbList.Count; ++i)
{
    if (i > 0 && lbList[i - 1].score != lbList[i].score)
        ++rank;
    lbList[i].rank = rank;
}

如果您需要lbList作为IEnumerable<>，那么：

var lbList = a.
    GroupBy(q => q.score).
    OrderByDescending(g => g.Key).
    SelectMany(
        (group, index) => group.Select(s => {
            s.rank = index + 1;
            return s;
        });

在LinQ中将相同的排名分配给相同的分数

2 个答案:

序言

排序