Linq按多个字段分组并展平列表

Question

我得到了以下数据

title |有用

ttitle1|是

ttitle1|是

ttitle1|无

ttitle2|是

我想把上面的数据分组并压平，这样我就得到了以下结果：

标题|有用计数|无效计数

tttitle1|2|1

tttitle2|1|0

尝试过这个，但没有产生正确的结果：

 var query = (from r in ratings
                    group r by new { r.ArticleTitle, r.Useful } into results
                    group results by new { results.Key.ArticleTitle } into results2
                    from result in results2
                    select new
                    {
                        Title = result.Key.ArticleTitle,
                        Yes = result.Select(i => i.Useful).Count(),
                        No = result.Select(i => i.Useful == false).Count()
                    });

有什么帮助吗？

Answer 1

在我看来，唯一的问题是分组两次。我希望这能奏效：

var query = from rating in ratings
            group rating by rating.ArticleTitle into g
            select new
            {
                Title = g.Key,
                Yes = g.Count(r => r.Useful),
                No = g.Count(r => !r.Useful)
            };

或者不在查询表达式形式中：

var query = ratings.GroupBy(r => r.ArticleTitle,
                            (key, rs) => new
                            {
                                Title = key,
                                Yes = rs.Count(r => r.Useful),
                                No = rs.Count(r => !r.Useful)
                            });

Answer 2

您不需要分组两次就可以获得所需的结果。一个分组就可以了：

var query = (from r in ratings
             group r by new { r.ArticleTitle } into g
             from result in groups
             select new
             {
                 Title = result.Key,
                 Yes = result.Select(i => i.Useful).Count(),
                 No = result.Select(i => !i.Useful).Count()
             });