c# - Using LINQ, how would you filter out all but one item of a particular criteria from a list? -

i realize title isn't clear here's example:

i have list of objects 2 properties, , b.

public class item {     public int { get; set; }     public int b { get; set; } }  var list = new list<item> {     new item() { = 0, b = 0 },     new item() { = 0, b = 1 },     new item() { = 1, b = 0 },     new item() { = 2, b = 0 },     new item() { = 2, b = 1 },     new item() { = 2, b = 2 },     new item() { = 3, b = 0 },     new item() { = 3, b = 1 }, } 

using linq, what's elegant way collapse = 2 items first = 2 item , return along other items? expected result.

var list = new list<item> {     new item() { = 0, b = 0 },     new item() { = 0, b = 1 },     new item() { = 1, b = 0 },     new item() { = 2, b = 0 },     new item() { = 3, b = 0 },     new item() { = 3, b = 1 }, } 

i'm not linq expert , have "manual" solution expressiveness of linq , curious see if done better.

how about:

var collapsed = list.groupby(i => i.a)                     .selectmany(g => g.key == 2 ? g.take(1) : g); 

the idea first group them a , select again (flattening .selectmany) in case of key being 1 want collapse, take first entry take(1).