linq加入两个具有动态大小的列表

Question

我有两个列表，List<Collection> collections和List<Invoice>发票。两者都有一个CurrencyID字段和一个Value字段。我需要的是将这两个列表按货币ID分组，并将收集的值减去发票价值。而且这只是在匹配的情况下，否则，无论在哪个列表中都会有不匹配的情况，我会在最终列表中需要它。例如：

invoices  collections   final 
30 EUR    10 USD   10 EUR 
40 CAN    20 EUR   40 USD  
50 USD    50 JPN   40 CAN 
            50 JPN 

Answer 1

考虑以下类和列表：

class Collection { public string CurrencyID; public Int32 Value; } 
class Invoice { public string CurrencyID; public Int32 Value; } 

... 

List<Collection> collections = new List<Collection> { 
    new Collection() {CurrencyID="USD", Value=10}, 
    new Collection() {CurrencyID="EUR", Value=20}, 
    new Collection() {CurrencyID="JPN", Value=50} 
}; 

List<Invoice> invoices = new List<Invoice> { 
    new Invoice() {CurrencyID="USD", Value=50}, 
    new Invoice() {CurrencyID="EUR", Value=30}, 
    new Invoice() {CurrencyID="CAN", Value=40} 
}; 

你可以得到你想要做什么，两个简单的查询，然后使用Union将它们结合起来。

var result1 = (from i in invoices 
       let o = collections.SingleOrDefault(x => x.CurrencyID == i.CurrencyID) 
       select new 
       { 
        CurrencyID = i.CurrencyID, 
        Value = i.Value - (o != null ? o.Value : 0) 
       }).ToList(); 

var result2 = from c in collections 
       where !result1.Any(x => x.CurrencyID == c.CurrencyID) 
       select new 
       { 
       CurrencyID = c.CurrencyID, 
       Value = c.Value 
       }; 

var result = result1.Union(result2).OrderBy (r => r.Value); 

结果