Question

我有一些LINQ可以带回一些数据。它由两个属性ChannelType和ChannelName组成。有时，由于尚未设置频道，因此频道类型将为null，并且其计数仅为1。

LINQ查询：

var channels = (from channel in db.UriData
                join device in db.Devices on channel.SerialNumber equals device.SerialNumber
                join active in db.ActiveChannels on channel.ChannelName equals active.ChannelName
                where channel.ChannelName.Contains(active.ChannelName) && 
                device.Active &&
                channel.SerialNumber == serial
                select new { channel.ChannelName, channel.ChannelType }).Distinct().ToList().OrderByDescending(x => x.ChannelName);

从LINQ查询返回的数据：

{ ChannelName = "v1", ChannelType = null }
{ ChannelName = "v1", ChannelType = "Electricity" }
{ ChannelName = "v2", ChannelType = null }
{ ChannelName = "v2", ChannelType = "Electricity" }
{ ChannelName = "v3", ChannelType = null }
{ ChannelName = "v3", ChannelType = "Electricity" }
{ ChannelName = "v4", ChannelType = null }

从数据中，您将看到ChannelName有两个值，一个是null，一个不是。我希望能够选择Max()值，因此在有两个通道名称的地方，我可以忽略null。 Max()将处理null的单个ChannelName，如数据中的第一项所示。

如何选择Max()并删除多个ChannelName的空值。例如，如果我们使用数据中所示的ChannelName v1，则可以看到有两个v1。我想获取Max（）并忽略/删除存在多个v1的null值。

我假设我可以通过另一个LINQ查询来做到这一点，例如：

var c = channels.Select(x => new { x.ChannelName, x.ChannelType }).Max();

预期结果：

{ ChannelName = "v1", ChannelType = "Electricity" }
{ ChannelName = "v2", ChannelType = "Electricity" }
{ ChannelName = "v3", ChannelType = "Electricity" }
{ ChannelName = "v4", ChannelType = null }

TIA

Answer 1

执行此操作的一种方法是使用GroupBy。基本上，您将所有通道按名称（键）分组，然后对所有值进行排序，以获取第一个符合您条件的通道：

var result = channels
    .GroupBy(i => i.ChannelName)
    .Select(i => new 
    { 
        ChannelName = i.Key, 
        ChannelType = i.OrderByDescending(v => v.ChannelType)
                       .First()
                       .ChannelType
    });

Answer 2

尝试以下操作：

            var results = channels.Where(x => x.ChannelType != null)
                .Select(x => new { index = int.Parse(x.ChannelName.Replace("v", "")), channel = x })
                .GroupBy(x => x.channel.ChannelType)
                .Select(x => x.OrderByDescending(y => y.index))
                .Select(x => x.FirstOrDefault().channel)
                .ToList();

Answer 3

var _channels = new List<(string, string)>();

foreach(var c in channels)
{
    var channeltypes = channels.Where(x => x.ChannelName == c.ChannelName && x.ChannelType != null);
    if(channeltypes.Any())
    {
        _channels.Add((channeltypes[0].ChannelName, channeltypes[0].ChannelType));
    } else {
        _channels.Add((c.ChannelName, null));
    }
}

LINQ-如果count> 1，则选择两个值中的最大值

3 个答案: