无法基于两列旋转 C# 数据表

Posted 2023-04-12

【中文标题】无法基于两列旋转 C# 数据表

【英文标题】：Unable to pivot C# datatable based on two columns

【发布时间】：2021-06-23 21:55:08

【问题描述】：

我有一个包含三列的 C# 数据表。表格是这样的：

DataTable dt = new DataTable();
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Type", typeof(string));
            dt.Columns.Add("Val", typeof(string));


             dt.Rows.Add("One", "NZ", "100");
        dt.Rows.Add("One", "EN", "200");
        dt.Rows.Add("One", "CA", "300");
        dt.Rows.Add("Two", "ZM", "400");
        dt.Rows.Add("Two", "SA", "200");
        dt.Rows.Add("Two", "NZ", "440");
        dt.Rows.Add("Two", "EN", "990");
        dt.Rows.Add("Three", "IN", "660");
        dt.Rows.Add("Three", "CH", "994");
        dt.Rows.Add("Three", "JP", "900");
        dt.Rows.Add("Three", "CA", "50");
        dt.Rows.Add("Four", "WI", "330");

旋转后的预期输出：

           NZ     EN    CA       ZM      SA       IN       CH     JP      WI
One        100    200   300
Two        440    990            400     200
Three                   50                        660       994    900 
Four                                                                       330

我想旋转 Type 列，但基于 Name 列。

我正在尝试使用以下代码对其进行旋转并出现错误：

public static DataTable PivotDataTable(DataTable table, string columnX,
                                                    params string[] columnsToIgnore)
        
            //Create a DataTable to Return
            DataTable returnTable = new DataTable();

            if (columnX == "")
                columnX = table.Columns[0].ColumnName;

            //Add a Column at the beginning of the table

            returnTable.Columns.Add(columnX);

            //Read all DISTINCT values from columnX Column in the provided DataTale
            List<string> columnXValues = new List<string>();

            //Creates list of columns to ignore
            List<string> listColumnsToIgnore = new List<string>();
            if (columnsToIgnore.Length > 0)
                listColumnsToIgnore.AddRange(columnsToIgnore);

            if (!listColumnsToIgnore.Contains(columnX))
                listColumnsToIgnore.Add(columnX);

            foreach (DataRow dr in table.Rows)
            
                string columnXTemp = dr[columnX].ToString();
                //Verify if the value was already listed
                if (!columnXValues.Contains(columnXTemp))
                
                    //if the value id different from others provided, add to the list of 
                    //values and creates a new Column with its value.
                    columnXValues.Add(columnXTemp);
                    returnTable.Columns.Add(columnXTemp);
                
                else
                
                    //Throw exception for a repeated value
                    throw new Exception("The inversion used must have " +
                                        "unique values for column " + columnX);
                
            

            //Add a line for each column of the DataTable

            foreach (DataColumn dc in table.Columns)
            
                if (!columnXValues.Contains(dc.ColumnName) &&
                    !listColumnsToIgnore.Contains(dc.ColumnName))
                
                    DataRow dr = returnTable.NewRow();
                    dr[0] = dc.ColumnName;
                    returnTable.Rows.Add(dr);
                
            

            //Complete the datatable with the values
            for (int i = 0; i < returnTable.Rows.Count; i++)
            
                for (int j = 1; j < returnTable.Columns.Count; j++)
                
                    returnTable.Rows[i][j] =
                      table.Rows[j - 1][returnTable.Rows[i][0].ToString()].ToString();
                
            

            return returnTable;
        

我得到的错误：'所使用的反转必须具有列类型的唯一值'

我该如何解决这个错误？

【问题讨论】：

是的，异常就在您自己的代码中。为避免这种情况，columnXValues.Contains(columnXTemp) 必须始终评估为 false 所以要么使用不同的条件，要么使用满足您已经编写的条件的数据。

【参考方案1】：

使用此扩展方法：

// pivot a DataTable to a new DataTable
// By field is row id and grouping key
// Over field creates new column names
// Value field is value for new columns
public static DataTable PivotByOverWith(this DataTable dt, string ByRowFieldName, string OverColFieldName, string WithValueFieldName) 
    var res = new DataTable();
    if (dt.Rows.Count > 0) 
        var dtg = dt.AsEnumerable().GroupBy(r => r[ByRowFieldName], r => new  Over = r[OverColFieldName].ToString(), With = r[WithValueFieldName] );

        var hasByRow = ByRowFieldName != OverColFieldName;
        if (hasByRow)
            res.Columns.Add(new DataColumn(ByRowFieldName, dt.Columns[ByRowFieldName].DataType));

        var valueDataType = dt.Columns[WithValueFieldName].DataType;
        var colNames = dtg.SelectMany(rg => rg.Select(r => r.Over)).Distinct();
        foreach (var n in colNames)
            res.Columns.Add(n, valueDataType);

        foreach (var rg in dtg) 
            var newr = res.NewRow();
            if (hasByRow)
                newr[ByRowFieldName] = rg.Key;
            foreach (var r in rg)
                newr[r.Over] = r.With;
            res.Rows.Add(newr);
        
    
    return res;

你可以计算你的答案：

var ans = dt.PivotByOverWith("Name", "Type", "Val");

【参考方案2】：

这就是我之前做过数百次的方式：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace ConsoleApplication1

    class Program
    
        static void Main(string[] args)
        
            DataTable dt = new DataTable();
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Type", typeof(string));
            dt.Columns.Add("Val", typeof(int));


            dt.Rows.Add("One", "NZ", 100);
            dt.Rows.Add("One", "EN", 200);
            dt.Rows.Add("One", "CA", 300);
            dt.Rows.Add("Two", "ZM", 400);
            dt.Rows.Add("Two", "SA", 200);
            dt.Rows.Add("Two", "NZ", 440);
            dt.Rows.Add("Two", "EN", 990);
            dt.Rows.Add("Three", "IN", 660);
            dt.Rows.Add("Three", "CH", 994);
            dt.Rows.Add("Three", "JP", 900);
            dt.Rows.Add("Three", "CA", 50);
            dt.Rows.Add("Four", "WI", 330);

            string[] types = dt.AsEnumerable().Select(x => x.Field<string>("Type")).Distinct().OrderBy(x => x).ToArray();

            DataTable pivot = new DataTable();
            pivot.Columns.Add("Name");
            foreach (string type in types)
            
                pivot.Columns.Add(type, typeof(int));
            

            var groups = dt.AsEnumerable().GroupBy(x => x.Field<string>("Name"));

            foreach (var group in groups)
            
                DataRow newRow = pivot.Rows.Add();
                newRow["Name"] = group.Key;
                foreach (DataRow row in group)
                
                    newRow[row.Field<string>("Type")] = row.Field<int>("Val");