Lamdba表达式以过滤相同数目的对

试试这个:

// your original data
var Items = new List<Item>();

// those items with status 0
var itemsToBeRemoved = Items.Where(x => !x.Status);

// remove those first
Items.RemoveAll(itemsToBeRemoved.Contains);

// now find the things with the same name, order by date, get the first one.
var theOtherItemsToBeRemoved = itemsToBeRemoved.Select(x => 
    Items.Where(y => y.Name == x.Name).OrderBy(y => y.Created).FirstOrDefault()
).ToList();

// now remove the items found
Items.RemoveAll(theOtherItemsToBeRemoved.Contains);

我想不出任何符合您需求的LINQ扩展方法,但您可以通过嵌套循环轻松实现它,如下所示:

  // Data generation
  var items = new List<Item>();
  for (int i = 0; i < 7; i++)
    items.Add(new Item() { Id = i + 1, Dt = DateTime.Parse("9/11/2018 14:00:00").AddMinutes(i), Name = "A1", Status = true });
  items[3].Name = "A2";
  items[4].Name = "A3";
  items[5].Status = false;

  // It's also good to make sure that elements are in correct order
  items = items.OrderBy(i => i.Dt).ToList();

  // Procedure, to execute your logic
  for (int i = 0; i < items.Count(); i++)
  {
    // If it has Status = true, then look for "enclosing" element with Status = false
    if(items[i].Status)
      for (int j = i + 1; j < items.Count(); j++)
      {
        if(!items[j].Status && items[j].Name == items[i].Name)
        {
          // Mark items, so we delete them (and recognize those with status 0 as used)
          items[i].Name = "";
          items[j].Name = "";
        }
      }
  }
  // Remove all marked elements
  items.RemoveAll(i => i.Name == "");

我不确定LINQ to Entity表达式,但是在内存中加载项之后,可以删除在数据库中被“标记”为已删除的项。

var items = await db.items.OrderBy(item => item.Created).ToListAsync();

var stillInItems = items.GroupBy(item => item.Name)
                        .Select(group => group.ToLookup(item => item.Status))
                        .SelectMany(lookup => 
                        {
                            var outItemsCount = lookup[false].Count();
                            return lookup[true].Skip(outItemsCount);
                        })
                        .ToList();

ROW_NUMBER 对于具有相同名称和状态的项,然后排除具有相同名称和状态的对应项的项 行\u编号

使用LINQ,您可以按 Name Status 0 然后归还所有 状态 1 正在跳过的计数 0 对象排序依据 Created . 如果还有更多 0 1. 姓名

var filtered = src
                .GroupBy(s => s.Name)
                .SelectMany(g => { // for each name group
                    var skipCount = g.Where(r => r.Status == 0).Count(); // count the 0 status
                    return g.Where(r => r.Status == 1).OrderBy(r => r.Created).Skip(skipCount); // return the 1 status without earliest matched to 0 status
                })
                .OrderBy(s => s.Id);

假设您只想删除每个名称中状态为true和false的第一个实例,我猜这是可行的:

// Create lookup
ILookup<string, Item> lookupItems = Items.OrderBy(ordBy => ordBy.Created)
                                         .ToLookup(l => l.Name);

// Iterate through your collection
Items.RemoveAll(item => lookupItems[item.Name].Any(lookupItem => !lookupItem.Status)
     ? lookupItems[item.Name].First(lookupItem => !lookupItem.Status).Id == item.Id || 
       lookupItems[item.Name].First(lookupItem => lookupItem.Status).Id == item.Id
     : false);