Linq查询来对每个组中的顶级项目进行分组和查询(Linq query to group items and query from the top item in each group)

Linq查询来对每个组中的顶级项目进行分组和查询(Linq query to group items and query from the top item in each group)

所以，我有一个看起来像这样的列表。 它基本上是一堆物品的状态历史记录，最近的状态代表当前状态。

Record Id State Date ===== === ========= ======= 1 A Waiting Jan 01 2 A InProgress Jan 02 3 A Finished Jan 03 4 B Waiting Jan 02 5 C Waiting Jan 01 6 C InProgress Jan 02 7 D Waiting Jan 01 8 D InProgress Jan 02

我正在寻找的是能够查询每个项目的“当前”状态。 例如，我想说：“给我所有的Ids都是'InProgress'”并且获得Id D和Id C，但不是Id A（因为它的最新状态是'已完成'）。

我知道我必须做一些分组和一些订购或Maxing，但我不能把它放在一起。

So, I have a list that looks something like this. Its basically a state history for a bunch of items, with the most recent state representing the current state.

Record Id State Date ===== === ========= ======= 1 A Waiting Jan 01 2 A InProgress Jan 02 3 A Finished Jan 03 4 B Waiting Jan 02 5 C Waiting Jan 01 6 C InProgress Jan 02 7 D Waiting Jan 01 8 D InProgress Jan 02

What I'm looking for is to be able to query the 'current' state for each item. For example, I'd like to say: "Give me all Ids are are 'InProgress'" and get Id D and Id C, but not Id A (because its latest state is 'Finished').

I know I've got to do some grouping and some ordering or Maxing, but I can't quite put it all together.

最满意答案

myList.GroupBy(m => m.Id) .Select(g => g.OrderByDescending(x => x.Date).First()) .Where(<your filter>); myList.GroupBy(m => m.Id) .Select(g => g.OrderByDescending(x => x.Date).First()) .Where(<your filter>);