从linq查询计算C＃中的运行总计

Question

I have spent a good few days learning linq and producing json results from my controller in mvc. I am now however stuck on an issue where I wish to rolling sum (cumulative sum) values of Y-Axis data to produce a year to date line chart.

My code at present to produce simple monthly data is as follows:

//Generic Json For Graphs
public JsonResult GetJSONYTD(int kpiID)
{
    var ViewData = 
        (from kpidata in departmentrepo.GetGraphData(kpiID)
         select new DepartmentOverviewDetailsViewModel.GraphJSONViewModel
         {
             XData = kpidata.Year.Year1 + "-" 
                     + kpidata.Month.Real_Month_Int + "-01",
             YData = kpidata.Value
         });

    var ChartData = ViewData.Select(
                        x => new object[] { x.XData, x.YData }).ToArray();

    return Json(ChartData, JsonRequestBehavior.AllowGet);
}

The above produces the following array:

[
 ["2011-10-01",0],
 ["2011-11-01",22],
 ["2011-12-01",22],
 ["2012-1-01",14],
 ["2012-2-01",14.4],
 ["2012-3-01",17.5],
 ["2012-4-01",20.3],
 ["2012-5-01",23.5],
 ["2012-6-01",24.5],
 ["2012-7-01",26.5]
]

I would like to output:

[
 ["2011-10-01",0],
 ["2011-11-01",22],
 ["2011-12-01",44],
 ["2012-1-01",38],
 ["2012-2-01",52.4],
 etc
]

Any help?

Answer 1

Change your code to:

//Generic Json For Graphs

public JsonResult GetJSONYTD(int kpiID)
{
    var graphData = departmentrepo.GetGraphData(kpiID);
    var ViewData = (from kpidata in graphData

                    select new DepartmentOverviewDetailsViewModel.GraphJSONViewModel
                    {
                        XData = kpidata.Year.Year1 + "-" + kpidata.Month.Real_Month_Int + "-01",
                        YData = graphData.Where(x=>x.Date<=kpidata.Date).Sum(x=>x.Value)
                    });

    var ChartData = ViewData.Select(x => new object[] { x.XData, x.YData }).ToArray();

    return Json(ChartData, JsonRequestBehavior.AllowGet);
}

The above code will store in YData the sum of all data points that have a data less than or equal to the current date.

Answer 2

You can do this inline with Aggregate:

    var rollingSum = ViewData.Aggregate(
        // start with a list of a single model with value 0 (this avoids func having to deal with the empty list case
        seed: new[] { new DepartmentOverviewDetailsViewModel.GraphJSONViewModel { XData = string.Empty, YData = 0.0 } }.ToList(),
        // the aggregation function adds to the list a new tuple with the current date string
        // and a cumulative sum value
        func: (list, data) => {
            list.Add(new DepartmentOverviewDetailsViewModel.GraphJSONViewModel { XData = data.XData, YData = data.YData + list[list.Count - 1].YData });
            return list;
        }
    )
    .Skip(1) // skip the first dummy value we seeded the list with
    .ToArray();

Another option is to write a general purpose cumulative sum function and then used that:

public static class MyEnumerableExtensions {

    public static IEnumerable<double> CumulativeSum(this IEnumerable<double> @this) {
        var sum = 0;
        foreach (var value in @this) { sum += value; yield return sum; }
    }

}

// then to compute the sum you want
var rollingSum = ViewData.Select(m => m.YData).CumulativeSum();
var rollingSumWithDates = ViewData.Zip(rollingSum, (m, sum) => new DepartmentOverviewDetailsViewModel.GraphJSONViewModel { XData = m.XData, YData = sum })
    .ToArray();