是否可以使用LINQ旋转数据？

我是LINQ的新手,但我想知道是否可以使用LINQ从以下布局转移数据:

CustID | OrderDate | Qty
1      | 1/1/2008  | 100
2      | 1/2/2008  | 200
1      | 2/2/2008  | 350
2      | 2/28/2008 | 221
1      | 3/12/2008 | 250
2      | 3/15/2008 | 2150

进入这样的事情:

CustID  | Jan- 2008 | Feb- 2008 | Mar - 2008 |
1       | 100       | 350       |  250
2       | 200       | 221       | 2150

Amy B.. 184

像这样的东西？

List myList = GetCustData();

var query = myList
    .GroupBy(c => c.CustId)
    .Select(g => new {
        CustId = g.Key,
        Jan = g.Where(c => c.OrderDate.Month == 1).Sum(c => c.Qty),
        Feb = g.Where(c => c.OrderDate.Month == 2).Sum(c => c.Qty),
        March = g.Where(c => c.OrderDate.Month == 3).Sum(c => c.Qty)
    });

GroupBy在Linq中,它与SQL不同.在SQL中,您获得密钥和聚合(行/列形状).在Linq中,您可以获得键和任何元素作为键的子元素(层次结构形状).要进行透视,您必须将层次结构投影回您选择的行/列形式.

像这样的东西？

List myList = GetCustData();

var query = myList
    .GroupBy(c => c.CustId)
    .Select(g => new {
        CustId = g.Key,
        Jan = g.Where(c => c.OrderDate.Month == 1).Sum(c => c.Qty),
        Feb = g.Where(c => c.OrderDate.Month == 2).Sum(c => c.Qty),
        March = g.Where(c => c.OrderDate.Month == 3).Sum(c => c.Qty)
    });

GroupBy在Linq中,它与SQL不同.在SQL中,您获得密钥和聚合(行/列形状).在Linq中,您可以获得键和任何元素作为键的子元素(层次结构形状).要进行透视,您必须将层次结构投影回您选择的行/列形式.

我使用linq扩展方法回答了类似的问题:

// order s(ource) by OrderDate to have proper column ordering
var r = s.Pivot3(e => e.custID, e => e.OrderDate.ToString("MMM-yyyy")
    , lst => lst.Sum(e => e.Qty));
// order r(esult) by CustID

(+)通用实现
( - )绝对比David B慢

任何人都可以改进我的实现(即方法执行列和行的排序)？

我认为,最好的方法是使用查找:

var query =
    from c in myList
    group c by c.CustId into gcs
    let lookup = gcs.ToLookup(y => y.OrderDate.Month, y => y.Qty)
    select new
    {
        CustId = gcs.Key,
        Jan = lookup[1].Sum(),
        Feb = lookup[2].Sum(),
        Mar = lookup[3].Sum(),
    };