使用Linq统计平均值

Question

I have a class named HardwarePerformance contain these fields: time,cpuUsagePercent,memoryUsagePercent,diskUsage,diskRead,diskWrite,latency. I had fill a List object to contain the not statistics data. I need to calculating the average value for all these fields in a Linq command. I don't know how to get the average value with Linq. Follow is the code I wrote (It's incorrect of course).

var _hardwarePerf = (from _stats in _statsList 
                    where _time>=DateTime.Parse("2012-04-04 00:00:00")
                        &&_time<=DateTime.Parse("2012-04-04 11:00:00") 
                    select new {
                           Latency = _stats.latency, 
                           CpuUsagePercent = _stats.cpuUsagePercent, 
                           MemoryUsagePercent = _stats.memoryUsagePercent, 
                           DiskUsage = _stats.diskUsage, DiskRead = _stats.diskRead, 
                           DiskWrite = _stats.diskWrite
                    }).Average(Latency => Latency.Latency);

The syntax of this code is correct. But I want to calculating all the average value at the same time, how do I write my code?

Answer 1

There is no built-in method for this in LINQ. If you don't mind that you will be iterating the collection several times, and assuming an anonymous object is okay for you, you can do something like this (where filteredStats contains the data you want to average, probably filtered by time):

var averages =
    new
    {
        Latency = filteredStats.Average(x => x.Latency),
        CpuUsagePercent = filteredStats.Average(x => x.CpuUsagePercent),
        …
    };

If that's not what you want, you will probably have to calculate the averages on your own.

Answer 2

The following calculates all the averages in one iteration, although it's a lot of code.

Note that I've assumed time is a property on your stats object, otherwise your select where time doesn't make much sense.

var _hardwareAccumulator =
    _statsList
        .Where(s =>
            s.time >= DateTime.Parse("2012-04-04 00:00:00") &&
            s.time <= DateTime.Parse("2012-04-04 11:00:00"))
        .Aggregate(
            new
            {
                count = 0,
                cpuUsagePercent = 0.0,
                memoryUsagePercent = 0.0,
                diskUsage = 0.0,
                diskRead = 0.0
            },
            (acc, s) =>
                new
                {
                    count = acc.count + 1,
                    cpuUsagePercent =
                        acc.cpuUsagePercent + s.cpuUsagePercent,
                    memoryUsagePercent =
                        acc.memoryUsagePercent + s.memoryUsagePercent,
                    diskUsage =
                        acc.diskUsage + s.diskUsage,
                    diskRead =
                        acc.diskRead + s.diskRead
                }
            );
var _hardwarePerf = new
{
    cpuUsagePercent =
        _hardwareAccumulator.cpuUsagePercent / _hardwareAccumulator.count,
    memoryUsagePercent =
        _hardwareAccumulator.memoryUsagePercent / _hardwareAccumulator.count,
    diskUsage =
        _hardwareAccumulator.diskUsage / _hardwareAccumulator.count,
    diskRead =
        _hardwareAccumulator.diskRead / _hardwareAccumulator.count
};

Answer 3

You either nee to do that in separate statements or you could do it in this not very intuitive way:

var averages = statsList.Where(s => s.time >= new DateTime(2012, 4, 4) && s.time <= new DateTime(2012, 4, 04, 11, 0, 0))
            .GroupBy(s => 1)
            .Select(grp => new
            {
                Latency = grp.Average(s => s.latency),
                CpuUsagePercent = grp.Average(s => s.cpuUsagePercent),
                MemoryUsagePercent = grp.Average(s => s.memoryUsagePercent),
                DiskUsage = grp.Average(s => s.diskUsage),
                DiskRead = grp.Average(s => s.diskRead),
                DiskWrite = grp.Average(s => s.diskWrite)
            }).FirstOrDefault();

Note that .GroupBy(s => 1) just to be able to calculate the average for each property. Also note that i've removed the underlines from your property names and added time to your class.

The other approach is easier to read:

var theStats = statsList.Where(s => s.time >= new DateTime(2012, 4, 4) && s.time <= new DateTime(2012, 4, 04, 11, 0, 0));
var Latency = theStats.Average(s => s.latency);
var CpuUsagePercent = theStats.Average(s => s.cpuUsagePercent);
// ....

Answer 4

You can use "Group By" then you can use an average projection to calculate.

var query = from _stats in _statsList 
    group _stats by new {
               Latency = _stats.latency, 
               CpuUsagePercent = _stats.cpuUsagePercent, 
               MemoryUsagePercent = _stats.memoryUsagePercent, 
               DiskUsage = _stats.diskUsage, 
               DiskRead = _stats.diskRead, 
               DiskWrite = _stats.diskWrite

    } into myGroup
    select new {
        AverageVal = myGroup.Average(x => x.Value),
        CpuUsagePercent = myGroup.Key.CpuUsagePercent,
        ... // the rest of your projection
};

LINQ Average