c# - LINQ 中的分组、求和

Question

假设我有下表:

user type amount
2    a    10
2    b    20
2    c    40
3    a    15
3    b    20
3    c    45

我想将 (c) 数量替换为 (c - (a+b)) 按用户和类型分组，我该怎么做？谢谢

Answer 1

这里有一个方法:

更新(现在使用Sum):

from item in table
group item by item.user into g
let a = (from i in g where i.type == "a" select i.amount).Sum()
let b = (from i in g where i.type == "b" select i.amount).Sum()
let c = (from i in g where i.type == "c" select i.amount).Sum()
select c - (a + b);