如何檢查使用foreach時DataTable行是否發生了變化？

Question

我有以下代碼：

int sequence = 1; //This is incremented every time the Account changes 
int numberOfItems; //This is reset after the Account changes 
decimal totalAmount = 0m; //This is reset after the Account changes 
string prevRow; //not sure how to handle this 

foreach(DataRow row in dt.Rows) 
{ 
    //I am stuck here 
    if(row["Account"]) == prevRow) 
    { 
    numberOfItems++; 
    totalAmount += Convert.ToDecimal(row["TotalAmount"]); 
    } 
    else 
    { 
    //reset everything and increase sequence 
    numberOfItems = 0; 
    totalAmount = 0m; 
    sequence++ 
    } 

} 

我的初始表可以包含數據：

ABC，50.0
ABC，50.0
DEF，60.0
GHI，70.0

當循環使用for，abc的numberOfItems應爲2，def爲1，ghi爲1。 abc的總金額應爲100.0，def爲60.0，ghi爲70.0。 abc的順序應該是1，def的順序應該是2，ghi的順序應該是3。

我在運行for循環時注意到的第一件事是，它跳過第一個表中的一堆行，所以當我在else中創建第二個表時，numberOfItems和totalAmount仍然是0.第二個表應該是類似：

ABC，100，如圖2所示，1
DEF，60，1，2個
GHI，70，1,3

其中在CSV值的最後一個數字是序列和數目在此之前是每個帳戶的numberOfItems。

for (int i = 0; i < dt.Rows.Count; i++) 
      { 
       DataRow row = dt.Rows[i]; 
       DataRow prevRow = i > 0 ? dt.Rows[i - 1] : null; 

       if (prevRow != null && row[1] == prevRow[1]) 
       { 
        numberOfItems++; 
        totalAmount += Convert.ToDecimal(row[2]); 
        row[3] = "D"; 
        row[4] = c; 
        row[5] = sequence; 

       } 
       else 
       { 
        dt2.Rows.Add("N", 
         c, 
         row[1], 
         row[2], 
         row[3], 
         numberOfItems, 
         totalAmount, 
         sequence); 

        numberOfItems = 0; 
        totalAmount = 0m; 
        sequence++; 
       } 
      } 

Answer 1

A foreach行不知道它是前一行。那麼你爲什麼不簡單地使用for-loop？

for(int i = 0; i < dt.Rows.Count; i++) 
{ 
    DataRow row = dt.Rows[ i ]; 
    DataRow prevRow = i > 0 ? dt.Rows[ i - 1 ] : null; 

    if(prevRow != null && row["Account"] == prevRow["Account"]) 
    { 
     // ... 
    } 
} 

---

現在你已經更新了你的問題，我會建議使用Linq-To-DataSet：

var groups = dt.AsEnumerable() 
    .GroupBy(r => r.Field<String>("Account")) 
    .Select((g, i) => new { 
     Account = g.Key, 
     TotalAmount = g.Sum(r => r.Field<double>("TotalAmount")), 
     Count = g.Count(), 
     Id = i + 1, 
    }); 

foreach (var grp in groups) 
    Console.WriteLine("{0},{1},{2},{3}" 
     ,grp.Account, grp.TotalAmount, grp.Count, grp.Id); 

請注意，您需要添加using System.Linq。

Answer 2

您可以使用DataTable.GetChanges

鏈接：http://msdn.microsoft.com/en-us/library/k2552649.aspx

var changeTable = table.GetChanges(); 
foreach(var item in changeTable.Rows) 
{ 
..... 

} 

對於修改的行，你可以使用參數DataRowState.Modified

table.GetChanges(DataRowState.Modified); 

Answer 3

int sequence = 1; //This is incremented every time the Account changes 
int numberOfItems; //This is reset after the Account changes 
decimal totalAmount = 0m; //This is reset after the Account changes 
string prevRow = null; //not sure how to handle this 

foreach(DataRow row in dt.Rows) 
{ 
    //I am stuck here 
    if((row["Account"]) == prevRow) 
    { 
    numberOfItems++; 
    totalAmount += Convert.ToDecimal(row["TotalAmount"]); 
    } 
    else 
    { 
    //reset everything and increase sequence 
    numberOfItems = 0; 
    totalAmount = 0m; 
    sequence++; 
    } 
    prevRow = row["Account"]; 

} 

請注意，我已經把一個;在順序遞增之後。

Answer 4

int sequence = 1; //This is incremented every time the Account changes 
int numberOfItems; //This is reset after the Account changes 
decimal totalAmount = 0m; //This is reset after the Account changes 
String prevAccount == ""; //not sure how to handle this 

foreach(DataRow row in dt.Rows) 
{ 
    //I am stuck here 
    if(row["Account"] == prevAccount) 
    { 
     numberOfItems++; 
     totalAmount += Convert.ToDecimal(row["TotalAmount"]); 
    } 
    else 
    { 
     //reset everything and increase sequence 
     numberOfItems = 0; 
     totalAmount = 0m; 
     sequence++; 
    } 
    prevAccount = row["Account"]; 
}