Develop Reference

Merging DataTables with Condition

I would like to merge DataTables in a list using sum or average depending on conditions. For example:
private DataTable getData(List<DataTable> datas, string[] KeyColumnNames, string valueCol)
{
List<DataTable> dataTables = datas;
//if datas has 3 dataTables in it : dt1, dt2, dt3
// then I want to create another dataTable dtAll which will have the sum of
// valueCol of all three datatables for the row which will be conditioned using
// KeyColumnNames (can be multiple Primary keys)
return dataTable;
}
Consider all datatables to be exactly same but different values as they are tables from similar schemas but different data centers.
Thanks.

I would do
List<DataTable> dataTableList = dtList;
DataTable unionDataTable = new DataTable();
for(int i = 0; i < dtList.Count; i++)
unionDataTable = Union(unionDataTable, dtList[i], "UnionDataTable");
where the Union method is defined by something like the following
public static DataTable Union(DataTable First, DataTable Second, string strReturnedTableName)
{
// Result table.
DataTable table = new DataTable(strReturnedTableName);
// Build new columns.
DataColumn[] newcolumns = new DataColumn[First.Columns.Count];
for (int i = 0; i < First.Columns.Count; i++)
newcolumns[i] = new DataColumn(First.Columns[i].ColumnName, First.Columns[i].DataType);
// Add new columns to result table.
table.Columns.AddRange(newcolumns);
table.BeginLoadData();
// Load data from first table.
foreach (DataRow row in First.Rows)
table.LoadDataRow(row.ItemArray, true);
// Load data from second table.
foreach (DataRow row in Second.Rows)
table.LoadDataRow(row.ItemArray, true);
table.EndLoadData();
return table;
}
I hope this helps.
Edit. You can pass an Action in to the method and use this in the foreach blocks to do what you want.

Your question is way too vague to provide any actual code but you want to do a LINQ Join. It works about the same as a SQL join. This question shows joins in both query and method syntax How to do a join in linq to sql with method syntax? also you can look at the msdn docs here; http://msdn.microsoft.com/en-us/library/bb311040.aspx

Copy DataTable.Rows to DataRow[]. Faster way then Select() with the same functionality?

I have now a problem with a very old system of ours. (!It is more then 7 years old and I have no budget and resources to make bigger change in the structure, so the decision to improve the old logic as many as we can.!)
We have an own written gridcontrol. Basically it is like a normal ASP.NET grid, you can add, change, delete elements.
The problem is that the grid has a BindGrid() method, where for further usage, the rows of the datasource table copied into a DataRow[]. I need to keep the DataRow[], but I would like to implement the best way to copy the source from the the table into the array.
The current solution:
DataRow[] rows = DataSource.Select("1=1", SortOrderString);
As I experienced so far, if I need to get a specified sort, that could be the best way (I'm also interested if it has a quicker way or not.)
BUT there are some simplified pages, where the SortOrder is not needed.
So I could make two method one for the sort order and one for without.
The real problem is the second one:
DataRow[] rows = DataSource.Select("1=1");
Because it is very slow. I made some test and it is kind of 15 times slower then the CopyTo() solution:
DataRow[] rows = new DataRow[DataSource.Rows.Count];
DataSource.Rows.CopyTo(rows,0);
I would like to use the faster way, BUT when I made the tests some old function simply crashed. It seems, there is an other difference, what I only noticed now:
The Select() gets the rows like the RowChanges are accepted.
So if I deleted a row, and I do not use the AcceptRowChanges() (I can't do that unfortunately), then with Select("1=1") the row is in the DataSource but not in the DataRow[].
With a simple .CopyTo() the row is there, and that is a bad news for me.
My questions are:
1) Is the Select("1=1") the best way to get the rows by the RowChanges? (I doubt a bit, because it is like 6 year old part)
2) And if 1) is not, is it possible to achieve a faster way with the same result than the .Select("1=1") ?
UPDATE:
Here is a very basic test app, what I used for speedtesting:
DataTable dt = new DataTable("Test");
dt.Columns.Add("Id", typeof (int));
dt.Columns.Add("Name", typeof(string));
for (int i = 0; i < 10000; i++)
{
DataRow row = dt.NewRow();
row["ID"] = i;
row["Name"] = "Name" + i;
dt.Rows.Add(row);
}
dt.AcceptChanges();
DateTime start = DateTime.Now;
DataRow[] rows = dt.Select();
/*DataRow[] rows = new DataRow[dt.Rows.Count];
dt.Rows.CopyTo(rows,0);*/
Console.WriteLine(DateTime.Now - start);

You can call Select without an argument: DataRow[] allRows = DataSource.Select(); That would be for sure more efficient than "1=1" since that applies a pointless RowFilter.
Another way is using Linq-To-DataSet to order and filter the DataTable. That isn't more efficient but more readable and maintainable.
I have yet no example or measurement, but it is obvious that a RowFilter with "1=1" is more expensive than none. Select is implemented in this way:
public Select(DataTable table, string filterExpression, string sort, DataViewRowState recordStates)
{
this.table = table;
this.IndexFields = table.ParseSortString(sort);
this.indexDesc = Select.ConvertIndexFieldtoIndexDesc(this.IndexFields);
// following would be omitted if you would use DataSource.Select() without "1=1"
if (filterExpression != null && filterExpression.Length > 0)
{
this.rowFilter = new DataExpression(this.table, filterExpression);
this.expression = this.rowFilter.ExpressionNode;
}
this.recordStates = recordStates;
}
If you want to be able to select also the rows that are currently not accepted, you can use the overload of Select:
DataRow[] allRows = DataSource.Select("", "", DataViewRowState.CurrentRows | DataViewRowState.Deleted);
This will select all rows inclusive the rows that are deleted even if AcceptChanges was not called yet.

Delete row from datatable where first column does not contain (some string)

I have DataTable with the following columns:
ClientID date numberOfTransactions price
ClientID is of type string and I need to ensure that its contents include "A-" and "N6" for every value in the table.
I need to delete all rows from the DataTable where this first column (ClientID) does not contain both "A-" and "N6" (some totals and other unnecessary data). How can I select and delete these rows specifically from the DataTable?
I know this:
foreach (DataRow row in table.Rows) // Loop over the rows.
{
//Here should come part "if first column contains mentioned values
}
I also know this
If (string.Contains("A-") == true && string.Contains("N6") == true)
{
//Do something
}
I need help how to implement this for first column of each row.

Try this:
EDIT: Totally messed up that last line, so if you tried it, try it now that I made it not stupid. =)
List<int> IndicesToRemove = new List<int>();
DataTable table = new DataTable(); //Obviously, your table will already exist at this point
foreach (DataRow row in table.Rows)
{
if (!(row["ClientID"].ToString().Contains("A-") && row["ClientID"].ToString().Contains("N6")))
IndicesToRemove.Add(table.Rows.IndexOf(row));
}
IndicesToRemove.Sort();
for (int i = IndicesToRemove.Count - 1; i >= 0; i--) table.Rows.RemoveAt(IndicesToRemove[i]);

try using this,
assuming dt as your Datatabe object and ClientID as your first column (hence using ItemArray[0])
for(int i=0; i<dt.Rows.Count; i++)
{
temp = dt.Rows[i].ItemArray[0].ToString();
if (System.Text.RegularExpressions.Regex.IsMatch(temp, "A-", System.Text.RegularExpressions.RegexOptions.IgnoreCase) || System.Text.RegularExpressions.Regex.IsMatch(temp, "N6", System.Text.RegularExpressions.RegexOptions.IgnoreCase))
{
dt.Rows.RemoveAt(i);
i--;
}
}
Simple and straight forward solution... hope it helps

this should be more efficient, both in lines of Code and Time, try this :)
for(int x=0; x<table.Rows.Count;)
{
if (!table.Rows[x].ItemArray[0].contains("A-") && !table.Rows[x].ItemArray[0].contains("N6"))
table.Rows.RemoveAt(x);
else x++;
}
Happy Coding

Preface: C.Barlow's existing answer is awesome, this is just another route someone could take.
This is one way to do it where you never have to loop all the way through the original table (by taking advantage of the DataTable.Select() method):
DataTable table = new DataTable(); // This would be your existing DataTable
// Grab only the rows that meet your criteria using the .Select() method
DataRow[] newRows = table.Select("ClientID LIKE '%A-%' AND ClientID LIKE '%N6%'");
// Create a new table with the same schema as your existing one.
DataTable newTable = table.Clone();
foreach (DataRow r in newRows)
{
// Dump the selected rows into the table.
newTable.LoadDataRow(r.ItemArray, true);
}
And now you have a DataTable with only the rows you want. If necessary, at this point you could clear out the original table and replace it with the contents of the new one:
table.Clear();
table = newTable.Copy();
Edit: I thought of a memory optimization last night, you can just overwrite the existing table once you have the rows you need, which avoids the need for the temporary table.
DataTable table = new DataTable(); // This would be your existing DataTable
// Grab only the rows that meet your criteria using the .Select() method
DataRow[] newRows = table.Select("ClientID LIKE '%A-%' AND ClientID LIKE '%N6%'");
// Clear out the old table
table.Clear();
foreach (DataRow r in newRows)
{
// Dump the selected rows into the table.
table.LoadDataRow(r.ItemArray, true);
}

Copy rows from one Datatable to another DataTable?

How can I copy specific rows from DataTable to another Datable in c#? There will be more than one row.

foreach (DataRow dr in dataTable1.Rows) {
if (/* some condition */)
dataTable2.Rows.Add(dr.ItemArray);
}
The above example assumes that dataTable1 and dataTable2 have the same number, type and order of columns.

Copy Specified Rows from Table to another
// here dttablenew is a new Table and dttableOld is table Which having the data
dttableNew = dttableOld.Clone();
foreach (DataRow drtableOld in dttableOld.Rows)
{
if (/*put some Condition */)
{
dtTableNew.ImportRow(drtableOld);
}
}

Try This
String matchString="ID0001"//assuming we have to find rows having key=ID0001
DataTable dtTarget = new DataTable();
dtTarget = dtSource.Clone();
DataRow[] rowsToCopy;
rowsToCopy = dtSource.Select("key='" + matchString + "'");
foreach (DataRow temp in rowsToCopy)
{
dtTarget.ImportRow(temp);
}

Check this out, you may like it (previously, please, clone table1 to table2):
table1.AsEnumerable().Take(recodCount).CopyToDataTable(table2,LoadOption.OverwriteChanges);
Or:
table1.AsEnumerable().Where ( yourcondition ) .CopyToDataTable(table2,LoadOption.OverwriteChanges);

Supported in: 4, 3.5 SP1, you can now just call a method on the object.
DataTable dataTable2 = dataTable1.Copy()

As a result of the other posts, this is the shortest I could get:
DataTable destTable = sourceTable.Clone();
sourceTable.AsEnumerable().Where(row => /* condition */ ).ToList().ForEach(row => destTable.ImportRow(row));

I've created an easy way to do this issue
DataTable newTable = oldtable.Clone();
for (int i = 0; i < oldtable.Rows.Count; i++)
{
DataRow drNew = newTable.NewRow();
drNew.ItemArray = oldtable.Rows[i].ItemArray;
newTable.Rows.Add(drNew);
}

I needed to copy rows from multiple tables with the same structure into a new table to be used as a datasource for datagridview:
// Generate DataTable[] alltables from multiple datatables
DataTable newTable = alltables[0].Clone();
foreach (DataTable dt in alltables)
{
for (int i = 0; i < dt.Rows.Count; i++)
newTable.Rows.Add(dt.Rows[i].ItemArray);
}

below sample would be the fastest way to copy one row.
each cell is being copied based on the column name.
in case you dont need a specific cell to copy then have a try catch or add if.
if your going to copy more than 1 row then loop the code below.
DataRow dr = dataset1.Tables[0].NewRow();
for (int i = 0; i < dataset1.Tables[1].Columns.Count; i++)
{
dr[dataset1.Tables[1].Columns[i].ColumnName] = dataset1.Tables[1].Rows[0][i];
}
datasetReport.Tables[0].Rows.Add(dr);
dataset1.Tables[1].Rows[0][i]; change the index 0 to your specified row index or you can use a variable if your going to loop or if its going to be logical

private void CopyDataTable(DataTable table){
// Create an object variable for the copy.
DataTable copyDataTable;
copyDataTable = table.Copy();
// Insert code to work with the copy.
}

To copy whole datatable just do this:
DataGridView sourceGrid = this.dataGridView1;
DataGridView targetGrid = this.dataGridView2;
targetGrid.DataSource = sourceGrid.DataSource;

For those who want single command SQL query for that:
INSERT INTO TABLE002
(COL001_MEM_ID, COL002_MEM_NAME, COL002_MEM_ADD, COL002_CREATE_USER_C, COL002_CREATE_S)
SELECT COL001_MEM_ID, COL001_MEM_NAME, COL001_MEM_ADD, COL001_CREATE_USER_C, COL001_CREATE_S
FROM TABLE001;
This query will copy data from TABLE001 to TABLE002 and we assume that both columns had different column names.
Column names are mapped one-to-one like:
COL001_MEM_ID -> COL001_MEM_ID
COL001_MEM_NAME -> COL002_MEM_NAME
COL001_MEM_ADD -> COL002_MEM_ADD
COL001_CREATE_USER_C -> COL002_CREATE_USER_C
COL002_CREATE_S -> COL002_CREATE_S
You can also specify where clause, if you need some condition.

There is better way to do this.
DataTable targetDataTable = new DataTable();
targetDataTable = changedColumnMetadata.AsEnumerable().Where(dataRow => entityName.Equals(dataRow["EntityName"])).CopyToDataTable();
Please try this and let me know in case of any issues.

You can do it calling the DataTable.Copy() method, for example:
DataSet ds = new DataSet();
System.Data.DataTable dt = new System.Data.DataTable();
dt = _BOSearchView.DS.Tables[BusLib.TPV.TableName.SearchView].Copy();
ds.Tables.Add(dt);
UltGrdSaleExcel.SetDataBinding(ds, dt.TableName, true);

use Merge, this will append all rows of newDataTable with oldDateTale
oldDateTale.Merge(newDataTable);

C#: retrieve the first n records from a DataTable

I have a DataTable that contains 2000 records.
How would you retrieve the first 100 records in the DataTable?

If it implements IEnumerable<T>:
var first100 = table.Take(100);
If the type in question only implements IEnumerable, you can use the Cast extention method:
var first100 = table.Cast<Foo>().Take(100);

This works for DB2.
select * from table
fetch first 100 rows only;

and for mysql: select * from table limit 100

You could use something like this, but restrict the foreach loop to 100 records.

And to make the list full, here is the statement for MS SQL:
Select top 5 * from MyTable2
And some other methods with MS SQL can be found here.

To get a list of the top n records in C# using the 2.0 framework:
DataTable dt = new DataTable();
var myRows = new List<DataRow>();
//no sorting specified; take straight from the top.
for (int i = 0; i < 100; i++)
{
myRows.Add(dt.Rows[i]);
}