DataTable 行列转换 将原来的行表转化成交叉表，无对应值赋默认值，用于统计显示或报表

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DataTable tt = GetCrossTable(CreateDT());
GridView1.DataSource = tt;
GridView1.DataBind();
}
}

//创建DataTable
protected DataTable CreateDT()
{
DataTable tblDatas = new DataTable("Datas");
//数据列
tblDatas.Columns.Add("姓名", Type.GetType("System.String"));
tblDatas.Columns.Add("科目", Type.GetType("System.String"));
tblDatas.Columns.Add("分数", Type.GetType("System.Int32"));

tblDatas.Rows.Add(new object[] { "张三", "语文", 89 });
tblDatas.Rows.Add(new object[] { "张三", "数学", 90 });
tblDatas.Rows.Add(new object[] { "张三", "英语", 79 });
tblDatas.Rows.Add(new object[] { "张三", "地理", 70 });
tblDatas.Rows.Add(new object[] { "张三", "生物", 95 });

tblDatas.Rows.Add(new object[] { "李四", "语文", 87 });
tblDatas.Rows.Add(new object[] { "李四", "英语", 86 });
tblDatas.Rows.Add(new object[] { "李四", "地理", 82 });

tblDatas.Rows.Add(new object[] { "王五", "语文", 81 });
tblDatas.Rows.Add(new object[] { "王五", "数学", 70 });
tblDatas.Rows.Add(new object[] { "王五", "英语", 88 });
tblDatas.Rows.Add(new object[] { "王五", "生物", 96 });
return tblDatas;
}

/// <summary>
/// 将DataTable的第二列的值转化为列（即将原来的行表，转化成交叉表，没有对应值则默认"0"）
/// </summary>
/// <param name="dt">必须三列，第三列为值</param>
/// <returns></returns>
public static DataTable GetCrossTable(DataTable dt)
{
if (dt == null || dt.Columns.Count != 3 || dt.Rows.Count == 0)
{
return dt;
}
else
{
DataTable result = new DataTable();
result.Columns.Add(dt.Columns[0].ColumnName);
DataTable dtColumns = dt.DefaultView.ToTable("dtColumns", true, dt.Columns[1].ColumnName);
for (int i = 0; i < dtColumns.Rows.Count; i++)
{
string colName;
if (dtColumns.Rows[1][0] is DateTime)
{
colName = Convert.ToDateTime(dtColumns.Rows[i][0]).ToString();
}
else
{
colName = dtColumns.Rows[i][0].ToString();
}
result.Columns.Add(colName);
result.Columns[i + 1].DefaultValue = "0";
}
DataRow drNew = result.NewRow();
drNew[0] = dt.Rows[0][0];
string rowName = drNew[0].ToString();
foreach (DataRow dr in dt.Rows)
{
string colName = dr[1].ToString();
double dValue = Convert.ToDouble(dr[2]);
if (dr[0].ToString().Equals(rowName, StringComparison.CurrentCultureIgnoreCase))
{
drNew[colName] = dValue.ToString();
}
else
{
result.Rows.Add(drNew);
drNew = result.NewRow();
drNew[0] = dr[0];
rowName = drNew[0].ToString();
drNew[colName] = dValue.ToString();
}
}
result.Rows.Add(drNew);
return result;
}
}