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how to add two datatables dt1=2 column ,dt2=3 column, into one datatable dt3=5 column

how to add two datatables?
(dt1=name,phone_number)
and
(dt2=address,cityname)
Result:
(dt3=name,phone_number,address,cityname)

Ruben, you will need some primary key in order to combine both tables unless you are 100% sure that both data tables have the same number of rows and they will always be stored in the correct order.
There is a similar question answered and the link is: Combining n DataTables into a Single DataTable
Here goes the content of the provided link:
"The table has repeating primary keys after the Merge because no primary-key was defined. So either specify the PK or try this method here which i've written from scratch(so it's not really tested):
public static DataTable MergeAll(this IList<DataTable> tables, String primaryKeyColumn)
{
if (!tables.Any())
throw new ArgumentException("Tables must not be empty", "tables");
if(primaryKeyColumn != null)
foreach(DataTable t in tables)
if(!t.Columns.Contains(primaryKeyColumn))
throw new ArgumentException("All tables must have the specified primarykey column " + primaryKeyColumn, "primaryKeyColumn");
if(tables.Count == 1)
return tables[0];
DataTable table = new DataTable("TblUnion");
table.BeginLoadData(); // Turns off notifications, index maintenance, and constraints while loading data
foreach (DataTable t in tables)
{
table.Merge(t); // same as table.Merge(t, false, MissingSchemaAction.Add);
}
table.EndLoadData();
if (primaryKeyColumn != null)
{
// since we might have no real primary keys defined, the rows now might have repeating fields
// so now we're going to "join" these rows ...
var pkGroups = table.AsEnumerable()
.GroupBy(r => r[primaryKeyColumn]);
var dupGroups = pkGroups.Where(g => g.Count() > 1);
foreach (var grpDup in dupGroups)
{
// use first row and modify it
DataRow firstRow = grpDup.First();
foreach (DataColumn c in table.Columns)
{
if (firstRow.IsNull(c))
{
DataRow firstNotNullRow = grpDup.Skip(1).FirstOrDefault(r => !r.IsNull(c));
if (firstNotNullRow != null)
firstRow[c] = firstNotNullRow[c];
}
}
// remove all but first row
var rowsToRemove = grpDup.Skip(1);
foreach(DataRow rowToRemove in rowsToRemove)
table.Rows.Remove(rowToRemove);
}
}
return table;
}
You can call it in this way:
var tables = new[] { tblA, tblB, tblC };
DataTable TblUnion = tables.MergeAll("c1");
Used this sample data:
var tblA = new DataTable();
tblA.Columns.Add("c1", typeof(int));
tblA.Columns.Add("c2", typeof(int));
tblA.Columns.Add("c3", typeof(string));
tblA.Columns.Add("c4", typeof(char));
var tblB = new DataTable();
tblB.Columns.Add("c1", typeof(int));
tblB.Columns.Add("c5", typeof(int));
tblB.Columns.Add("c6", typeof(string));
tblB.Columns.Add("c7", typeof(char));
var tblC = new DataTable();
tblC.Columns.Add("c1", typeof(int));
tblC.Columns.Add("c8", typeof(int));
tblC.Columns.Add("c9", typeof(string));
tblC.Columns.Add("c10", typeof(char));
tblA.Rows.Add(1, 8500, "abc", 'A');
tblA.Rows.Add(2, 950, "cde", 'B');
tblA.Rows.Add(3, 150, "efg", 'C');
tblA.Rows.Add(4, 850, "ghi", 'D');
tblA.Rows.Add(5, 50, "ijk", 'E');
tblB.Rows.Add(1, 7500, "klm", 'F');
tblB.Rows.Add(2, 900, "mno", 'G');
tblB.Rows.Add(3, 150, "opq", 'H');
tblB.Rows.Add(4, 850, "qrs", 'I');
tblB.Rows.Add(5, 50, "stu", 'J');
tblC.Rows.Add(1, 7500, "uvw", 'K');
tblC.Rows.Add(2, 900, "wxy", 'L');
tblC.Rows.Add(3, 150, "yza", 'M');
tblC.Rows.Add(4, 850, "ABC", 'N');
tblC.Rows.Add(5, 50, "CDE", 'O');
After DataTable.Merge in MergeAll:
After some modifications to join the rows in MergeAll:
Update
Since this question arose in one of the comments, if the only relation between two tables is the index of a DataRow in the table and you want to merge both tables according to the index:
public static DataTable MergeTablesByIndex(DataTable t1, DataTable t2)
{
if (t1 == null || t2 == null) throw new ArgumentNullException("t1 or t2", "Both tables must not be null");
DataTable t3 = t1.Clone(); // first add columns from table1
foreach (DataColumn col in t2.Columns)
{
string newColumnName = col.ColumnName;
int colNum = 1;
while (t3.Columns.Contains(newColumnName))
{
newColumnName = string.Format("{0}_{1}", col.ColumnName, ++colNum);
}
t3.Columns.Add(newColumnName, col.DataType);
}
var mergedRows = t1.AsEnumerable().Zip(t2.AsEnumerable(),
(r1, r2) => r1.ItemArray.Concat(r2.ItemArray).ToArray());
foreach (object[] rowFields in mergedRows)
t3.Rows.Add(rowFields);
return t3;
}
Sample:
var dt1 = new DataTable();
dt1.Columns.Add("ID", typeof(int));
dt1.Columns.Add("Name", typeof(string));
dt1.Rows.Add(1, "Jon");
var dt2 = new DataTable();
dt2.Columns.Add("Country", typeof(string));
dt2.Rows.Add("US");
var dtMerged = MergeTablesByIndex(dt1, dt2);
The result table contains three columns ID,Name,Country and a single row: 1 Jon US"
Source: Combining n DataTables into a Single DataTable
Last Access: 04-August-2016

First you can filter right column in to separate data datable
DataTable filterDatatable1= new DataTable();
DataTable filterDatatable2= new DataTable();
DataTable filterDatatable1= OriginaDatatable1.DefaultView.ToTable(false, "ColumnName1", "ColimnName2");
DataTable filterDatatable1= OriginaDatatable1.DefaultView.ToTable(false, "ColumnName1", "ColimnName2", "ColimnName3");
Then you can use merge function
DataTable dtAll = new DataTable();
dtAll.Merge(filterDatatable1);
dtAll.Merge(filterDatatable2);

compare and merge the datatable in C# [duplicate]

Let T1 and T2 are DataTables with following fields
T1(CustID, ColX, ColY)
T2(CustID, ColZ)
I need the joint table
TJ (CustID, ColX, ColY, ColZ)
How this can be done in C# code in a simple way? Thanks.

If you are allowed to use LINQ, take a look at the following example. It creates two DataTables with integer columns, fills them with some records, join them using LINQ query and outputs them to Console.
DataTable dt1 = new DataTable();
dt1.Columns.Add("CustID", typeof(int));
dt1.Columns.Add("ColX", typeof(int));
dt1.Columns.Add("ColY", typeof(int));
DataTable dt2 = new DataTable();
dt2.Columns.Add("CustID", typeof(int));
dt2.Columns.Add("ColZ", typeof(int));
for (int i = 1; i <= 5; i++)
{
DataRow row = dt1.NewRow();
row["CustID"] = i;
row["ColX"] = 10 + i;
row["ColY"] = 20 + i;
dt1.Rows.Add(row);
row = dt2.NewRow();
row["CustID"] = i;
row["ColZ"] = 30 + i;
dt2.Rows.Add(row);
}
var results = from table1 in dt1.AsEnumerable()
join table2 in dt2.AsEnumerable() on (int)table1["CustID"] equals (int)table2["CustID"]
select new
{
CustID = (int)table1["CustID"],
ColX = (int)table1["ColX"],
ColY = (int)table1["ColY"],
ColZ = (int)table2["ColZ"]
};
foreach (var item in results)
{
Console.WriteLine(String.Format("ID = {0}, ColX = {1}, ColY = {2}, ColZ = {3}", item.CustID, item.ColX, item.ColY, item.ColZ));
}
Console.ReadLine();
// Output:
// ID = 1, ColX = 11, ColY = 21, ColZ = 31
// ID = 2, ColX = 12, ColY = 22, ColZ = 32
// ID = 3, ColX = 13, ColY = 23, ColZ = 33
// ID = 4, ColX = 14, ColY = 24, ColZ = 34
// ID = 5, ColX = 15, ColY = 25, ColZ = 35

I wanted a function that would join tables without requiring you to define the columns using an anonymous type selector, but had a hard time finding any. I ended up having to make my own. Hopefully this will help anyone in the future who searches for this:
private DataTable JoinDataTables(DataTable t1, DataTable t2, params Func<DataRow, DataRow, bool>[] joinOn)
{
DataTable result = new DataTable();
foreach (DataColumn col in t1.Columns)
{
if (result.Columns[col.ColumnName] == null)
result.Columns.Add(col.ColumnName, col.DataType);
}
foreach (DataColumn col in t2.Columns)
{
if (result.Columns[col.ColumnName] == null)
result.Columns.Add(col.ColumnName, col.DataType);
}
foreach (DataRow row1 in t1.Rows)
{
var joinRows = t2.AsEnumerable().Where(row2 =>
{
foreach (var parameter in joinOn)
{
if (!parameter(row1, row2)) return false;
}
return true;
});
foreach (DataRow fromRow in joinRows)
{
DataRow insertRow = result.NewRow();
foreach (DataColumn col1 in t1.Columns)
{
insertRow[col1.ColumnName] = row1[col1.ColumnName];
}
foreach (DataColumn col2 in t2.Columns)
{
insertRow[col2.ColumnName] = fromRow[col2.ColumnName];
}
result.Rows.Add(insertRow);
}
}
return result;
}
An example of how you might use this:
var test = JoinDataTables(transactionInfo, transactionItems,
(row1, row2) =>
row1.Field<int>("TransactionID") == row2.Field<int>("TransactionID"));
One caveat: This is certainly not optimized, so be mindful when getting to row counts above 20k. If you know that one table will be larger than the other, try to put the smaller one first and the larger one second.

This is my code. Not perfect, but working good. I hope it helps somebody:
static System.Data.DataTable DtTbl (System.Data.DataTable[] dtToJoin)
{
System.Data.DataTable dtJoined = new System.Data.DataTable();
foreach (System.Data.DataColumn dc in dtToJoin[0].Columns)
dtJoined.Columns.Add(dc.ColumnName);
foreach (System.Data.DataTable dt in dtToJoin)
foreach (System.Data.DataRow dr1 in dt.Rows)
{
System.Data.DataRow dr = dtJoined.NewRow();
foreach (System.Data.DataColumn dc in dtToJoin[0].Columns)
dr[dc.ColumnName] = dr1[dc.ColumnName];
dtJoined.Rows.Add(dr);
}
return dtJoined;
}

this function will join 2 tables with a known join field, but this cannot allow 2 fields with the same name on both tables except the join field, a simple modification would be to save a dictionary with a counter and just add number to the same name filds.
public static DataTable JoinDataTable(DataTable dataTable1, DataTable dataTable2, string joinField)
{
var dt = new DataTable();
var joinTable = from t1 in dataTable1.AsEnumerable()
join t2 in dataTable2.AsEnumerable()
on t1[joinField] equals t2[joinField]
select new { t1, t2 };
foreach (DataColumn col in dataTable1.Columns)
dt.Columns.Add(col.ColumnName, typeof(string));
dt.Columns.Remove(joinField);
foreach (DataColumn col in dataTable2.Columns)
dt.Columns.Add(col.ColumnName, typeof(string));
foreach (var row in joinTable)
{
var newRow = dt.NewRow();
newRow.ItemArray = row.t1.ItemArray.Union(row.t2.ItemArray).ToArray();
dt.Rows.Add(newRow);
}
return dt;
}

I tried to do this in next way
public static DataTable JoinTwoTables(DataTable innerTable, DataTable outerTable)
{
DataTable resultTable = new DataTable();
var innerTableColumns = new List<string>();
foreach (DataColumn column in innerTable.Columns)
{
innerTableColumns.Add(column.ColumnName);
resultTable.Columns.Add(column.ColumnName);
}
var outerTableColumns = new List<string>();
foreach (DataColumn column in outerTable.Columns)
{
if (!innerTableColumns.Contains(column.ColumnName))
{
outerTableColumns.Add(column.ColumnName);
resultTable.Columns.Add(column.ColumnName);
}
}
for (int i = 0; i < innerTable.Rows.Count; i++)
{
var row = resultTable.NewRow();
innerTableColumns.ForEach(x =>
{
row[x] = innerTable.Rows[i][x];
});
outerTableColumns.ForEach(x =>
{
row[x] = outerTable.Rows[i][x];
});
resultTable.Rows.Add(row);
}
return resultTable;
}

Note that if you have a DataSet, you will need to steal the table from the Dataset with dataSet.Table[0]

How to perform a Union All on 2 DataTables

I am not using Entity Framework.
There are 2 Datatables, each with different no. of columns. There is one common column - ItemId
If it was Union, I would have used 'Merge', but don't know how to do a Union All for these 2 DataTables
public static void Main()
{
//First DataTable
DataTable dt1 = new DataTable();
dt1.Columns.Add("ItemId");
dt1.Columns.Add("Name");
dt1.Columns.Add("Color");
DataRow dr = dt1.NewRow();
dr["ItemId"] = "1";
dr["Name"] = "Name1";
dr["Color"] = "Color1";
dt1.Rows.Add(dr);
dr = dt1.NewRow();
dr["ItemId"] = "2";
dr["Name"] = "Name2";
dr["Color"] = "Color2";
dt1.Rows.Add(dr);
//Second DataTable
DataTable dt2 = new DataTable();
dt2.Columns.Add("ItemId");
dt2.Columns.Add("Name");
dt2.Columns.Add("Price");
DataRow dr2 = dt2.NewRow();
dr2["ItemId"] = "1";
dr2["Name"] = "Name1";
dr2["Price"] = "100";
dt2.Rows.Add(dr2);
dr2 = dt2.NewRow();
dr2["ItemId"] = "2";
dr2["Name"] = "Name3";
dr2["Price"] = "200";
dt2.Rows.Add(dr2);
}
Expected Output
ItemId Name Color Price
1 Name1 Color1
2 Name2 Color2
1 Name1 100
2 Name3 200

You can use DataTable.Merge()
If you have primary key in both the table then it will perform merge on primary key else it will directly append all the records.
In youe case make ItemID as primary key.

using System.Linq.Expressions;
......
var result1 = from row1 in dt1.AsEnumerable()
select new { Name = row1.Field<String>("Name"), Color = row1.Field<String>("Color"), Price = "" };
var result2 = from row1 in dt2.AsEnumerable()
select new { Name = row1.Field<String>("Name"), Color = "", Price = row1.Field<String>("Price") };
var res = result1.Concat(result2);
foreach (var item in res)
Console.WriteLine("{0} - {1} - {2}", item.Name, item.Color, item.Price);

Even though this question is years old, for anyone looking for another way to do this:
public static DataTable MergeTables(DataTable dt1, DataTable dt2)
{
DataTable dt3 = dt1.Clone();
foreach (DataColumn col in dt2.Columns)
{
string strColumnName = col.ColumnName;
int intColNum = 1;
while (dt3.Columns.Contains(strColumnName))
{
strColumnName = string.Format("{0}_{1}", col.ColumnName, ++intColNum);
}
dt3.Columns.Add(strColumnName, col.DataType);
}
var Mergered = dt1.AsEnumerable().Zip(dt2.AsEnumerable(), (r1, r2) => r1.ItemArray.Concat(r2.ItemArray).ToArray());
foreach (object[] rowFields in Mergered)
dt3.Rows.Add(rowFields);
return dt3;
}

Looping through 2 datatable and adding values to third

I have created 3 datatables
var dt1= new DataTable();
var dt2= new DataTable();
var dt3= new DataTable();
Then i loop
foreach (DataRow row1 in dt1.Rows)
{
dt3.Rows.Add(row1.ItemArray);
foreach (DataRow row2 in dt2.Rows)
{
var Id2 = row1["Id"];
var Id1= row2["Id"];
if (Id1 == Id2)
{
dt3.rows["Name"] = "" ; // doesnt work
}
}
}
As you can see that i loop on 2 datatables. Then in inner loop i check if the records matches. Now if the record matches then i want to update column "Name" on dt3 datatable.
I tried using
dt3.rows["Name"] = "" ;
But this doesnt work. I know the reason that its because i again need to loop on dt3 datatable and
assign values to column in that loop. But not sure how to do it and if there is even more better solution. I mean we can find id in dt3 datatable and then update value. But not sure how to do it
Is there more intelligent solution than looping on 2 table?

The first foreach is not needed. A simple DataTable.Copy will bring all the data and structure from the original table in the destination table. Then looping on the second table and Select on the third to find the matching rows and clear the name.
dt3 = dt1.Copy();
foreach (DataRow row2 in dt2.Rows)
{
DataRow[] match = dt3.Select("ID=" + row2["ID"].ToString());
if(match.Lenght > 0)
match[0]["Name"] = "" ;
}
Not sure if this is more performant from the other answers. Need to be tested

dt3.rows doesn't work, you want to change the name of the row that you have added now. This should work:
foreach (DataRow row1 in dt1.Rows)
{
DataRow newRow = dt3.Rows.Add(row1.ItemArray);
foreach (DataRow row2 in dt2.Rows)
{
var Id2 = row1["Id"];
var Id1 = row2["Id"];
if (Id1 == Id2)
{
newRow["Name"] = "new Name";
}
}
}

Try this:
foreach (DataRow row1 in dt1.Rows)
{
var row = dt3.Rows.Add(row1.ItemArray);
foreach (DataRow row2 in dt2.Rows)
{
var Id2 = row1["Id"];
var Id1= row2["Id"];
if (Id1 == Id2)
{
row["Name"] = ""; //maybe works
}
}
}

How about,
dt2Lookup = new HashSet(
dt2.AsEnumerable().Select(row => row.Field<int>("Id")));
dt3 = dt1.Clone();
forreach (var row In dt1.AsEnumerable())
{
var newRow = dt3.Rows.Add(row.ItemArray)
if (dt2lookup.Contains(row.Field<int>("Id"))
{
newRow.SetField("Name", string.Empty);
}
}
The HashSet should provide good lookup performance.

dt3 = dt1.Copy();
var RowDictionary = dt3.Rows.OfType<DataRow>().ToDictionary(dr => dr["ID"].ToString());
//replace by Dictionary<string,List<DataRow>> in case ID is not unique and fill it with a foreach loop.
foreach (DataRow row2 in dt2.Rows)
{
DataRow Match;
if (c.TryGetValue(row2["ID"].ToString(), out Match))
{
Match["Name"] = "";
}
}

You should call:
dt3.rows[dt3.rows.Count - 1].Columns["Name"] = "" ;

Combining n DataTables into a Single DataTable

All, there are some question on this, but I can't seem to extract enough information to solve the problem for my case. I extract an unknown number of tables into SQL Server 'Tab1', 'Tab2', 'Tab3', ... , 'TabN'. The columns in these tables are different, but the row definitions are the same. I need to pull all the data in from the Server into N DataTables and then combine these to form a single DataTable. What I do currently is
int nTmpVolTabIdx = 1;
strSqlTmp = String.Empty;
using (DataTable dataTableALL = new DataTable())
{
while (true)
{
string strTmpVolName = String.Format("Tab{0}", nTmpVolTabIdx);
strSqlTmp = String.Format("SELECT * FROM [{0}];", strTmpVolName);
// Pull the data from 'VolX' into a local DataTable.
using (DataTable dataTable = UtilsDB.DTFromDB(conn, strTmpVolName, strSqlTmp, false))
{
if (dataTable == null)
break;
else
dataTableALL.Merge(dataTable);
}
nTmpVolTabIdx++;
}
...
}
This merges the DataTables but they are miss-aligned (padding blank cells onto the appended data set). I could append the columns of the new DataTable via a loop; but is there an easier/nicer way to do this (perhaps using LINQ)?
Thanks for your time.
Edit. To provide the example data sets.
What I required is
The individual tables are
After the first Merge operation I have the following
Thanks again.

The table has repeating primary keys after the Merge because no primary-key was defined. So either specify the PK or try this method here which i've written from scratch(so it's not really tested):
public static DataTable MergeAll(this IList<DataTable> tables, String primaryKeyColumn)
{
if (!tables.Any())
throw new ArgumentException("Tables must not be empty", "tables");
if(primaryKeyColumn != null)
foreach(DataTable t in tables)
if(!t.Columns.Contains(primaryKeyColumn))
throw new ArgumentException("All tables must have the specified primarykey column " + primaryKeyColumn, "primaryKeyColumn");
if(tables.Count == 1)
return tables[0];
DataTable table = new DataTable("TblUnion");
table.BeginLoadData(); // Turns off notifications, index maintenance, and constraints while loading data
foreach (DataTable t in tables)
{
table.Merge(t); // same as table.Merge(t, false, MissingSchemaAction.Add);
}
table.EndLoadData();
if (primaryKeyColumn != null)
{
// since we might have no real primary keys defined, the rows now might have repeating fields
// so now we're going to "join" these rows ...
var pkGroups = table.AsEnumerable()
.GroupBy(r => r[primaryKeyColumn]);
var dupGroups = pkGroups.Where(g => g.Count() > 1);
foreach (var grpDup in dupGroups)
{
// use first row and modify it
DataRow firstRow = grpDup.First();
foreach (DataColumn c in table.Columns)
{
if (firstRow.IsNull(c))
{
DataRow firstNotNullRow = grpDup.Skip(1).FirstOrDefault(r => !r.IsNull(c));
if (firstNotNullRow != null)
firstRow[c] = firstNotNullRow[c];
}
}
// remove all but first row
var rowsToRemove = grpDup.Skip(1);
foreach(DataRow rowToRemove in rowsToRemove)
table.Rows.Remove(rowToRemove);
}
}
return table;
}
You can call it in this way:
var tables = new[] { tblA, tblB, tblC };
DataTable TblUnion = tables.MergeAll("c1");
Used this sample data:
var tblA = new DataTable();
tblA.Columns.Add("c1", typeof(int));
tblA.Columns.Add("c2", typeof(int));
tblA.Columns.Add("c3", typeof(string));
tblA.Columns.Add("c4", typeof(char));
var tblB = new DataTable();
tblB.Columns.Add("c1", typeof(int));
tblB.Columns.Add("c5", typeof(int));
tblB.Columns.Add("c6", typeof(string));
tblB.Columns.Add("c7", typeof(char));
var tblC = new DataTable();
tblC.Columns.Add("c1", typeof(int));
tblC.Columns.Add("c8", typeof(int));
tblC.Columns.Add("c9", typeof(string));
tblC.Columns.Add("c10", typeof(char));
tblA.Rows.Add(1, 8500, "abc", 'A');
tblA.Rows.Add(2, 950, "cde", 'B');
tblA.Rows.Add(3, 150, "efg", 'C');
tblA.Rows.Add(4, 850, "ghi", 'D');
tblA.Rows.Add(5, 50, "ijk", 'E');
tblB.Rows.Add(1, 7500, "klm", 'F');
tblB.Rows.Add(2, 900, "mno", 'G');
tblB.Rows.Add(3, 150, "opq", 'H');
tblB.Rows.Add(4, 850, "qrs", 'I');
tblB.Rows.Add(5, 50, "stu", 'J');
tblC.Rows.Add(1, 7500, "uvw", 'K');
tblC.Rows.Add(2, 900, "wxy", 'L');
tblC.Rows.Add(3, 150, "yza", 'M');
tblC.Rows.Add(4, 850, "ABC", 'N');
tblC.Rows.Add(5, 50, "CDE", 'O');
After DataTable.Merge in MergeAll:
After some modifications to join the rows in MergeAll:
Update
Since this question arose in one of the comments, if the only relation between two tables is the index of a DataRow in the table and you want to merge both tables according to the index:
public static DataTable MergeTablesByIndex(DataTable t1, DataTable t2)
{
if (t1 == null || t2 == null) throw new ArgumentNullException("t1 or t2", "Both tables must not be null");
DataTable t3 = t1.Clone(); // first add columns from table1
foreach (DataColumn col in t2.Columns)
{
string newColumnName = col.ColumnName;
int colNum = 1;
while (t3.Columns.Contains(newColumnName))
{
newColumnName = string.Format("{0}_{1}", col.ColumnName, ++colNum);
}
t3.Columns.Add(newColumnName, col.DataType);
}
var mergedRows = t1.AsEnumerable().Zip(t2.AsEnumerable(),
(r1, r2) => r1.ItemArray.Concat(r2.ItemArray).ToArray());
foreach (object[] rowFields in mergedRows)
t3.Rows.Add(rowFields);
return t3;
}
Sample:
var dt1 = new DataTable();
dt1.Columns.Add("ID", typeof(int));
dt1.Columns.Add("Name", typeof(string));
dt1.Rows.Add(1, "Jon");
var dt2 = new DataTable();
dt2.Columns.Add("Country", typeof(string));
dt2.Rows.Add("US");
var dtMerged = MergeTablesByIndex(dt1, dt2);
The result table contains three columns ID,Name,Country and a single row: 1 Jon US