C#内存表数据透视表生成

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

namespace GT
{
    /// <summary>
    /// 内存表透视表生成器 2020.3.10
    /// 调用方法new PivotTableGenerator(dt, "dq,xz,cw","fl","sl", "dq=地区,xz=小组,cw=财务").CreatePivotTable();
    /// </summary>
    public class PivotTableGenerator
    {

        private DataTable _source;
        private DataTable _result;

        string[] _fields;
        string _valueFileld;
        string _pivotField;
        private string _fieldRenameString;

        /// <summary>
        /// 内存表透视表生成器 构造方式
        /// 调用方法new PivotTableGenerator(dt, "dq,xz,cw","fl","sl", "dq=地区,xz=小组,cw=财务").CreatePivotTable();
        /// </summary>
        /// <param name="source"></param>
        /// <param name="fields">如</param>
        /// <param name=