Group By, Sum in LINQ

Question

suppose I have the following table:

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

I want to replace (c) amount with (c - (a+b)) grouping by the user and type, how could I do this? thanks

Answer 1

Here is a way:

UPDATE (now using 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);