我明白了！一个通用的 GroupByWithRollup。它仅按两列分组，但可以轻松扩展以支持更多。我可能会有另一个接受三列的版本。关键类/方法是 Grouping、GroupByMany() 和 GroupByWithRollup()。当您实际使用 GroupByWithRollup() 时，SubTotal() 和 GrandTotal() 方法是助手。下面是代码，后面是如何使用的例子。
/// <summary>
/// Represents an instance of an IGrouping<>. Used by GroupByMany(), GroupByWithRollup(), and GrandTotal().
/// </summary>
public class Grouping<TKey, TElement> : IGrouping<TKey, TElement>
{
public TKey Key { get; set; }
public IEnumerable<TElement> Items { get; set; }
public IEnumerator<TElement> GetEnumerator()
{
return Items.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return Items.GetEnumerator();
}
}
public static class Extensions
{
/// <summary>
/// Groups by two columns.
/// </summary>
/// <typeparam name="TElement">Type of elements to group.</typeparam>
/// <typeparam name="TKey1">Type of the first expression to group by.</typeparam>
/// <typeparam name="TKey2">Type of the second expression to group by.</typeparam>
/// <param name="orderedElements">Elements to group.</param>
/// <param name="groupByKey1Expression">The first expression to group by.</param>
/// <param name="groupByKey2Expression">The second expression to group by.</param>
/// <param name="newElementExpression">An expression that returns a new TElement.</param>
public static IQueryable<Grouping<TKey1, TElement>> GroupByMany<TElement, TKey1, TKey2>(this IOrderedQueryable<TElement> orderedElements,
Func<TElement, TKey1> groupByKey1Expression,
Func<TElement, TKey2> groupByKey2Expression,
Func<IGrouping<TKey1, TElement>, IGrouping<TKey2, TElement>, TElement> newElementExpression
)
{
// Group the items by Key1 and Key2
return from element in orderedElements
group element by groupByKey1Expression(element) into groupByKey1
select new Grouping<TKey1, TElement>
{
Key = groupByKey1.Key,
Items = from key1Item in groupByKey1
group key1Item by groupByKey2Expression(key1Item) into groupByKey2
select newElementExpression(groupByKey1, groupByKey2)
};
}
/// <summary>
/// Returns a List of TElement containing all elements of orderedElements as well as subTotals and a grand total.
/// </summary>
/// <typeparam name="TElement">Type of elements to group.</typeparam>
/// <typeparam name="TKey1">Type of the first expression to group by.</typeparam>
/// <typeparam name="TKey2">Type of the second expression to group by.</typeparam>
/// <param name="orderedElements">Elements to group.</param>
/// <param name="groupByKey1Expression">The first expression to group by.</param>
/// <param name="groupByKey2Expression">The second expression to group by.</param>
/// <param name="newElementExpression">An expression that returns a new TElement.</param>
/// <param name="subTotalExpression">An expression that returns a new TElement that represents a subTotal.</param>
/// <param name="totalExpression">An expression that returns a new TElement that represents a grand total.</param>
public static List<TElement> GroupByWithRollup<TElement, TKey1, TKey2>(this IOrderedQueryable<TElement> orderedElements,
Func<TElement, TKey1> groupByKey1Expression,
Func<TElement, TKey2> groupByKey2Expression,
Func<IGrouping<TKey1, TElement>, IGrouping<TKey2, TElement>, TElement> newElementExpression,
Func<IGrouping<TKey1, TElement>, TElement> subTotalExpression,
Func<IQueryable<Grouping<TKey1, TElement>>, TElement> totalExpression
)
{
// Group the items by Key1 and Key2
IQueryable<Grouping<TKey1, TElement>> groupedItems = orderedElements.GroupByMany(groupByKey1Expression, groupByKey2Expression, newElementExpression);
// Create a new list the items, subtotals, and the grand total.
List<TElement> results = new List<TElement>();
foreach (Grouping<TKey1, TElement> item in groupedItems)
{
// Add items under current group
results.AddRange(item);
// Add subTotal for current group
results.Add(subTotalExpression(item));
}
// Add grand total
results.Add(totalExpression(groupedItems));
return results;
}
/// <summary>
/// Returns the subTotal sum of sumExpression.
/// </summary>
/// <param name="sumExpression">An expression that returns the value to sum.</param>
public static int SubTotal<TKey, TElement>(this IGrouping<TKey, TElement> query, Func<TElement, int> sumExpression)
{
return query.Sum(group => sumExpression(group));
}
/// <summary>
/// Returns the subTotal sum of sumExpression.
/// </summary>
/// <param name="sumExpression">An expression that returns the value to sum.</param>
public static decimal SubTotal<TKey, TElement>(this IGrouping<TKey, TElement> query, Func<TElement, decimal> sumExpression)
{
return query.Sum(group => sumExpression(group));
}
/// <summary>
/// Returns the grand total sum of sumExpression.
/// </summary>
/// <param name="sumExpression">An expression that returns the value to sum.</param>
public static int GrandTotal<TKey, TElement>(this IQueryable<Grouping<TKey, TElement>> query, Func<TElement, int> sumExpression)
{
return query.Sum(group => group.Sum(innerGroup => sumExpression(innerGroup)));
}
/// <summary>
/// Returns the grand total sum of sumExpression.
/// </summary>
/// <param name="sumExpression">An expression that returns the value to sum.</param>
public static decimal GrandTotal<TKey, TElement>(this IQueryable<Grouping<TKey, TElement>> query, Func<TElement, decimal> sumExpression)
{
return query.Sum(group => group.Sum(innerGroup => sumExpression(innerGroup)));
}
还有一个使用它的例子：
class Program
{
static void Main(string[] args)
{
IQueryable<CustomObject> dataItems = (new[]
{
new CustomObject { City = "Seattle", Plan = "Plan B", Charges = 20 },
new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
new CustomObject { City = "Seattle", Plan = "Plan B", Charges = 20 },
new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
new CustomObject { City = "Seattle", Plan = "Plan A", Charges = 10 },
new CustomObject { City = "Portland", Plan = "Plan A", Charges = 10 },
new CustomObject { City = "Portland", Plan = "Plan A", Charges = 10 },
new CustomObject { City = "Portland", Plan = "Plan C", Charges = 30 },
new CustomObject { City = "Portland", Plan = "Plan C", Charges = 30 },
new CustomObject { City = "Portland", Plan = "Plan C", Charges = 30 }
}).AsQueryable();
List<CustomObject> results = dataItems.OrderBy(item => item.City).ThenBy(item => item.Plan).GroupByWithRollup(
item => item.City,
item => item.Plan,
(primaryGrouping, secondaryGrouping) => new CustomObject
{
City = primaryGrouping.Key,
Plan = secondaryGrouping.Key,
Count = secondaryGrouping.Count(),
Charges = secondaryGrouping.Sum(item => item.Charges)
},
item => new CustomObject
{
City = item.Key,
Plan = "All",
Count = item.SubTotal(subItem => subItem.Count),
Charges = item.SubTotal(subItem => subItem.Charges)
},
items => new CustomObject
{
City = "All",
Plan = "All",
Count = items.GrandTotal(subItem => subItem.Count),
Charges = items.GrandTotal(subItem => subItem.Charges)
}
);
foreach (var result in results)
Console.WriteLine(result);
Console.Read();
}
}
class CustomObject
{
public string City { get; set; }
public string Plan { get; set; }
public int Count { get; set; }
public decimal Charges { get; set; }
public override string ToString()
{
return String.Format("{0} - {1} ({2} - {3})", City, Plan, Count, Charges);
}
}