计算 DataTable 中列中先前行的总和

Question

我在计算 DataTable 等数据结构中某列中所有先前行的总和时遇到了一些问题

例如，我们有一个表，其中包含 “等待时间” 和 “突发时间” 列。

Waiting Time 的行值必须通过从 Burst Time 列中的前几行获取值来计算（如果有这样的 a.k.a 它不是我们当前计算值的第一行） p>

我怎样才能做到这一点？是否像使用Compute() 并传递适当的过滤字符串一样简单？

编辑：我想做的一个例子。

Answer 1

我做了一个例子。现在知道如何填充 DataTable，这就是我想出硬编码的原因。

public class Program
{
    public static void Main(string[] args)
    {
        dataSet = new DataSet();
        var dataTable = MakeTable();
        var columns = dataTable.Columns;

        Console.WriteLine("Defined Table");
        PrintDataTable(dataTable);

        foreach (DataRow dataTableRow in dataTable.Rows)
        {
            var id = dataTableRow["ID"];
            var burstTime = dataTable.Compute("Sum(BurstTime)", $"ID < {id}");
            dataTableRow["WaitingTime"] = burstTime;
        }

        Console.WriteLine();
        Console.WriteLine("Table After Operation");
        PrintDataTable(dataTable);

        Console.ReadLine();
    }

    private static void PrintDataTable(DataTable dataTable)
    {
        foreach (DataRow dataTableRow in dataTable.Rows)
        {
            Console.WriteLine($"{dataTableRow["Id"]}\t\t| {dataTableRow["WaitingTime"]}\t\t| {dataTableRow["BurstTime"]}");
        }
    }

    private static DataSet dataSet;

    private static DataTable MakeTable()
    {
        // Create a new DataTable.
        DataTable table = new DataTable("childTable");
        DataColumn column;
        DataRow row;

        // Create first column and add to the DataTable.
        column = new DataColumn();
        column.DataType = System.Type.GetType("System.Int32");
        column.ColumnName = "ID";
        column.AutoIncrement = true;
        column.Caption = "ID";
        column.ReadOnly = true;
        column.Unique = true;

        // Add the column to the DataColumnCollection.
        table.Columns.Add(column);

        // Create second column.
        column = new DataColumn();
        column.DataType = System.Type.GetType("System.String");
        column.ColumnName = "ChildItem";
        column.AutoIncrement = false;
        column.Caption = "ChildItem";
        column.ReadOnly = false;
        column.Unique = false;
        table.Columns.Add(column);

        // Create third column.
        column = new DataColumn();
        column.DataType = System.Type.GetType("System.Int32");
        column.ColumnName = "ParentID";
        column.AutoIncrement = false;
        column.Caption = "ParentID";
        column.ReadOnly = false;
        column.Unique = false;
        table.Columns.Add(column);

        // Create third column.
        column = new DataColumn();
        column.DataType = System.Type.GetType("System.Int32");
        column.ColumnName = "WaitingTime";
        column.AutoIncrement = false;
        column.Caption = "WaitingTime";
        column.ReadOnly = false;
        column.Unique = false;
        table.Columns.Add(column);

        // Create fourth column.
        column = new DataColumn();
        column.DataType = System.Type.GetType("System.Int32");
        column.ColumnName = "BurstTime";
        column.AutoIncrement = false;
        column.Caption = "BursTime";
        column.ReadOnly = false;
        column.Unique = false;
        table.Columns.Add(column);

        dataSet.Tables.Add(table);

        // Create three sets of DataRow objects, 
        // five rows each, and add to DataTable.
        for (int i = 0; i <= 4; i++)
        {
            row = table.NewRow();
            row["ID"] = i;
            row["ChildItem"] = "Item " + i;
            row["ParentID"] = 0;
            row["WaitingTime"] = 0;
            row["BurstTime"] = i;
            table.Rows.Add(row);
        }
        for (int i = 0; i <= 4; i++)
        {
            row = table.NewRow();
            row["ID"] = i + 5;
            row["ChildItem"] = "Item " + i;
            row["ParentID"] = 1;
            row["WaitingTime"] = 0;
            row["BurstTime"] = i + 5;
            table.Rows.Add(row);
        }
        for (int i = 0; i <= 4; i++)
        {
            row = table.NewRow();
            row["ID"] = i + 10;
            row["ChildItem"] = "Item " + i;
            row["ParentID"] = 2;
            row["WaitingTime"] = 0;
            row["BurstTime"] = i + 10;
            table.Rows.Add(row);
        }

        return table;
    }
}

我想对你来说最有趣的是：

foreach (DataRow dataTableRow in dataTable.Rows)
{
    var id = dataTableRow["ID"];
    var burstTime = dataTable.Compute("Sum(BurstTime)", $"ID < {id}");
    dataTableRow["WaitingTime"] = burstTime;
}

我认为这里最重要的是你必须想出自己的比较逻辑，即Compute(string, string)函数中的第二个参数。