Develop Reference

Checking value in column foreach row

The DataTable (dt) stores the retrieved values of carID's and makes so it stores like 3 rows within the DataTable, I also have another DataTable called dt2 which also stores carID's and makes, I am trying to loop through each row in the dt to see if any carID stored in the dt exists in any of the rows in dt2, here is what I have so far:
DataTable dt = w.getUserCars(userID);
foreach (DataRow dr in dt.Rows)
{
string carID = dr["carID"].ToString();
}
How do I do this?

You should be able to achieve this using DataTable.Select() method. You are on the right track. You just need to add the method to find the Row(s) in dt2.
DataTable dt = w.getUserCars(userID);
DataRow[] foundRows;
foreach (DataRow dr in dt.Rows)
{
string carID = dr["carID"].ToString();
foundRows = dt2.Select("carID = " + carID);
// do stuff here with foundRows
foreach (DataRow r in foundRows)
{
r.Delete();
}
}

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"] = "" ;

Delete Row From Data Table

I want to Delete the Multiple records from the DataTable
For example :
in my case PaperId is Repeating several Times.I want to Delete it all Duplicate records.
i have written code but loop is giving error
DataSet ds = new DataSet();
sqlDad.Fill(ds);
DataTable dt1 = new DataTable();
ds.Tables.Add(dt1);
dt1 = ds.Tables[0];
DataTable dt2 = new DataTable();
dt2 = dt1;
List<DataRow> rowsToDelete = new List<DataRow>();
foreach(DataRow dr in ds.Tables[0].Rows)
{
int r = ds.Tables[0].Columns.Count;
string x = dr.ItemArray[0].ToString();
int counter = 0;
foreach (DataRow dr1 in ds.Tables[0].Rows)
{
if (x == dr1.ItemArray[0].ToString())
{
counter++;
}
if (counter > 1)
{
rowsToDelete.Add(dr1);
foreach (DataRow row in rowsToDelete)
{
dt2.Rows.Remove(row);
}
dt2.AcceptChanges();
rowsToDelete.Clear();
}
}

Using the DefaultView of the DataTable and setting the sort order on the column that you don't want repeats to appear. You could loop over the rows and delete all the rows after the first one
// Work on the first table of the DataSet
DataTable dt1 = ds.Tables[0];
// No need to work if we have only 0 or 1 rows
if(dt1.Rows.Count <= 1)
return;
// Setting the sort order on the desidered column
dt1.DefaultView.Sort = dt1.Columns[0].ColumnName;
// Set an initial value ( I choose an empty string but you could set to something not possible here
string x = string.Empty;
// Loop over the row in sorted order
foreach(DataRowView dr in dt1.DefaultView)
{
// If we have a new value, keep it else delete the row
if(x != dr[0].ToString())
x = dr[0].ToString();
else
dr.Row.Delete();
}
// Finale step, remove the deleted rows
dt1.AcceptChanges();

Try This
DataRow[] rows;
rows=dataTable.Select("UserName = 'ABC'"); // UserName is Column Name
foreach(DataRow r in rows)
r.Delete();

If you want to remove the entire row from DataTable ,
try this
DataTable dt = new DataTable(); //User DataTable
DataRow[] rows;
rows = dt.Select("UserName = 'KarthiK'");
foreach (DataRow row in rows)
dt.Rows.Remove(row);

Looping through a DataTable

Well. I have a DataTable with multiple columns and multiple rows.
I want to loop through the DataTable dynamically basically the output should look as follows excluding the braces :
Name (DataColumn)
Tom (DataRow)
Peter (DataRow)
Surname (DataColumn)
Smith (DataRow)
Brown (DataRow)
foreach (DataColumn col in rightsTable.Columns)
{
foreach (DataRow row in rightsTable.Rows)
{
//output
}
}
I typed that out and noticed this would not work. Can someone please advice on a better way of doing this?

foreach (DataColumn col in rightsTable.Columns)
{
foreach (DataRow row in rightsTable.Rows)
{
Console.WriteLine(row[col.ColumnName].ToString());
}
}

foreach (DataRow row in dt.Rows)
{
foreach (DataColumn col in dt.Columns)
Console.WriteLine(row[col]);
}

Please try the following code below:
//Here I am using a reader object to fetch data from database, along with sqlcommand onject (cmd).
//Once the data is loaded to the Datatable object (datatable) you can loop through it using the datatable.rows.count prop.
using (reader = cmd.ExecuteReader())
{
// Load the Data table object
dataTable.Load(reader);
if (dataTable.Rows.Count > 0)
{
DataColumn col = dataTable.Columns["YourColumnName"];
foreach (DataRow row in dataTable.Rows)
{
strJsonData = row[col].ToString();
}
}
}

If you want to change the contents of each and every cell in a datatable then we need to Create another Datatable and bind it as follows using "Import Row". If we don't create another table it will throw an Exception saying "Collection was Modified".
Consider the following code.
//New Datatable created which will have updated cells
DataTable dtUpdated = new DataTable();
//This gives similar schema to the new datatable
dtUpdated = dtReports.Clone();
foreach (DataRow row in dtReports.Rows)
{
for (int i = 0; i < dtReports.Columns.Count; i++)
{
string oldVal = row[i].ToString();
string newVal = "{"+oldVal;
row[i] = newVal;
}
dtUpdated.ImportRow(row);
}
This will have all the cells preceding with Paranthesis({)

Add columnname and data from datatable to a dictionary? C#

I am looping through a datatable and currently I do
string customerId = row["CustomerId"].ToString();
string companyName = row["Company Name"].ToString();
Instead of declaring every variable how do I add these do a dictionary?
I was thinking something like:
foreach (DataRow row in customerTbl.Rows)
{
Dictionary<string, string> customerDictionary = new Dictionary<string, string>();
customerDictionary.Add(row[].ToString(), row[].ToString());
so yeah, how do I get the row name and value into there?
Thanks in advance.
EDIT:
I guess I didn't give you all information about what I am trying to do.
I query a database for a customer and populate a datatable with about 50 columns, I use the customer id to query another database and get the same customer from there. I then want to compare all 50 fields from both databases for the same customer and check if any field is different. I thought I could add the column name with the value in a dictionary for each row for each customer and then with two loops check if the values for the same key (column name) differs, is this a totally wrong approach?
having an if (customerId1 != customerId2 || customerName1 != customerName2 || and so on for 50 fields is not very good.

Are you looking for a generic solution to this kind of thing? If so does your DataTable always contain 2 columns where the first can be treated as the dictionary key and the second the value? If so, then simply use the column index instead of the column name
var customerDictionary = new Dictionary<string, string>();
foreach (DataRow row in customerTbl.Rows)
customerDictionary.Add(row[0].ToString(), row[1].ToString());
If the values in the customerId and CompanyName columns are never null then instead of using ToString(), you can cast the values to a string
customerDictionary.Add((string)row[0], (string)row[1]);
FYI, the DataTable has a search capability as well (the Find() method). If you set up a primary key column the search will be extremely fast and you may not need to copy the data from a DataTable to a Dictionary.
Edit : A complete working example of one way of doing this in C# code as per the OPs edited question
class Program
{
static void Main(string[] args)
{
var table1 = GetCustomersFromFirst();
var table2 = GetCustomersFromSecond();
foreach (DataRow row in table1.Rows)
{
var foundRows = table2.Select("CustomerId = " + (string)row[0]);
if (foundRows.Length == 1)
{
var foundRow = foundRows[0];
foreach (DataColumn col in table1.Columns)
{
var valueOfColumnFromTable1 = row[col.Ordinal].ToString();
var valueOfColumnFromTable2 = foundRow[col.Ordinal].ToString();
if (String.Compare(valueOfColumnFromTable1, valueOfColumnFromTable2) != 0)
{
//the colum values are not the same.
}
}
}
else
{
// Something is wrong since more than one matching record was found
// or no matching records were found.
}
}
}
static DataTable GetCustomersFromFirst()
{
var dt = GetInitializedCustomerDataTable();
var row = dt.NewRow();
row[0] = "1";
row[1] = "CompanyA";
dt.Rows.Add(row);
row = dt.NewRow();
row[0] = "2";
row[1] = "CompanyB";
dt.Rows.Add(row);
row = dt.NewRow();
row[0] = "3";
row[1] = "CompanyC";
dt.Rows.Add(row);
return dt;
}
static DataTable GetCustomersFromSecond()
{
var dt = GetInitializedCustomerDataTable();
var row = dt.NewRow();
row[0] = "1";
row[1] = "CompanyA";
dt.Rows.Add(row);
row = dt.NewRow();
row[0] = "2";
row[1] = "CompanyD";
dt.Rows.Add(row);
row = dt.NewRow();
row[0] = "3";
row[1] = "CompanyC";
dt.Rows.Add(row);
return dt;
}
static DataTable GetInitializedCustomerDataTable()
{
var dt = new DataTable();
dt.Columns.Add("CustomerId", typeof(string));
dt.Columns.Add("CompanyName", typeof(string));
return dt;
}
}
In the test data, the 2nd row does not match. So it should fall into the condition where the comment says:
//the colum values are not the same.
Personally, I'd look at doing this in the database itself.

Try this.
Dictionary<string, string> customerDictionary = new Dictionary<string, string>();
foreach (DataRow row in customerTbl.Rows)
{
if(row["CustomerId"] != null && customerDictionay.ContainsKey("CustomerId") == false)
{
customerDictionary.Add(row["CustomerID"].ToString(), row["CompanyName"] as string);
}
}

Just a question, what's the benefit of putting the values in a dictionary? You are basically just eliminating the need of writing .ToString() when accessing the values...i.e, instead of:
row["CustomerID"].ToString();
you write
customerDictionary["CustomerID"];
Or have I missed something?