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How To select Specific Column From DataTable in C#?

I have a dataTable with 4 columns ,
I want to select one column without foreach or any other expensive loop and my result must be a new data table with one column ,How can I do this;
DataTable leaveTypesPerPersonnel = LeaveGroup.GetLeaveTypesPerPersonnels(dtPersonnel.row);
leaveTypesPerPersonnel has this columns :
[ID,Guid,LeaveTypeID,Code]
I want Filter leaveTypesPerPersonnel wihtout foreach and get new datatable with just Column [ID]
NOTE: Output must be a Datatable With one column.

leaveTypesPerPersonnel.Columns.Remove("Guid");
leaveTypesPerPersonnel.Columns.Remove("LeaveTypeID");
leaveTypesPerPersonnel.Columns.Remove("Code");
or
DataTable dt= new DataView(leaveTypesPerPersonnel).ToTable(false,"ID");

You should be able to run a quick LINQ statement against the data table.
var results = (from item in leaveTypesPerPersonnel
select item.ID);
This will give you an IEnumerable if I remember correctly. It's not a DataTable, but might provide a solution to your problem as well.

Here is a try on how to search and convert the result to DataTable
var dataTable = leaveTypesPerPersonnel.Rows.Cast<DataRow>().ToList().Where(x=> x["ID"] == 21).CopyToDataTable().DefaultView.ToTable(false, "ID");
Or
var dataTable = leaveTypesPerPersonnel.Select("ID = 21").CopyToDataTable().DefaultView.ToTable(false, "ID");
Or
var dataTable = leaveTypesPerPersonnel.Rows.Cast<DataRow>().ToList().CopyToDataTable().DefaultView.ToTable(false, "ID");

Selecting a row from a particular column datatable without LINQ

My DataTable has the columns - Id, Name, Address. I need to select the column Address only WHERE ID = 7. How do I do this ? No LINQ please.
I was thinking of this -
DataView view = new DataView(MyDataTable);
DataTable distinctValues = view.ToTable(true, "ColumnA");
Now you can select.
DataRow[] myRows = distinctValues.Select();
//Get the desired answer by iterating myRows.
Is there a simpler way ?
thanks.

Well if you don't want to use LINQ, you can use a simple foreach loop:
DataTable distinctValues = view.ToTable(true, "ColumnA");
var myRows = new List<DataRow>();
foreach(DataRow row in distinctValues.Rows)
{
if(row["Id"].ToString() == "7") myRows.Add(row);
}

use select statement to get Data from a DataTable

I have DataTable containing three columns, Name, Date and DialedNumber. I want to get rows on the basis of DialedNumber column having phone number like 03001234567 ...
I am filing datatable with an method return type is datatable.
{
DataTable dt = filldata();
}
Problem is how to use select statement to get rows having number 03001234567 or some other telephone number ?

Try this Suppose you have a variable **string str** which is having that telephone number which you want to get from that data table then you can use this
{
DataTable dt = filldata();
DataRow[] resut = dt.Select("DialedNumber ='" + str + "'");
}
It will return you those rows having same telephone number in column DialedNumber.

If you want to filter from the start, not getting all table rows every time, you should adjust your SQL statement:
SELECT * FROM Table WHERE DialedNumber = #dialedNumber
and in C# use SqlCommand.Parameters.AddWithValue(...) to add the #dialedNumber parameter to the query.

Try to use Linq to DataTable like this
var results = from myRow in dt.AsEnumerable()
where myRow.Field<String>("DialedNumber") == "03001234567"
select myRow;

You can use Linq to DataSet:
string number = "03001234567";
var rows = dt.AsEnumerable()
.Where(r => r.Field<string>("DialedNumber").Contains(number));
You even can project rows into strongly typed objects:
var people = from r in dt.AsEnumerable()
where r.Field<string>("DialedNumber").Contains(number)
select new {
Name = r.Field<string>("Name"),
Date = r.Field<DateTime>("Date"),
DialedNumber = r.Field<string>("DialedNumber")
};
Note: if you want to check exact match of dialed number, then instead of Contains(number) (which is equivalent of LIKE) use == number.

Try like this
private void GetRowsByFilter()
{
DataTable table = DataSet1.Tables["Table1"];
// Presuming the DataTable has a column named Date.
string expression;
expression = "DialedNumber ='03001234567 '";
DataRow[] foundRows;
// Use the Select method to find all rows matching the filter.
foundRows = table.Select(expression);
// Print column 0 of each returned row.
for(int i = 0; i < foundRows.Length; i ++)
{
Console.WriteLine(foundRows[i][0]);
}
}
DataTable.Select Method

Using LINQ Query DataTable using partial column names

I have a DataTable with a variable number of columns.
I want to create a LINQ query that returns the data from the columns that start with a 'B_'.
I have a query that returns the columns names that start with 'B_'. It is below:
var arrayNames = (from DataColumn x in stationTable.Columns
where x.ColumnName.Contains("B_")
select x.ColumnName).ToArray();
Now that I have the column names how to I create a query using this array to return the data in the columns?
Thanks

You can create a DataView that hides the columns not in your list - that way you get to keep any type information:
var arrayNames = (from DataColumn x in stationTable.Columns
where !x.ColumnName.Contains("B_") // note the reversal
select x.ColumnName).ToArray();
DataView dv = new DataView(stationTable);
foreach (string colName in arrayNames)
dv.Table.Columns[colName].ColumnMapping = MappingType.Hidden

There are a couple of ways to approach this.
If you don't care about grouping the items by column type, this query accomplishes that:
var query = from DataColumn col in stationTable.Columns
from DataRow row in stationTable.Rows
where col.ColumnName.StartsWith("B_")
select row[col.ColumnName];
However, to maintain the grouping, you could use a lookup as follows:
var query = (from DataColumn col in stationTable.Columns
from DataRow row in stationTable.Rows
where col.ColumnName.StartsWith("B_")
select new { Row = row[col.ColumnName], col.ColumnName })
.ToLookup(o => o.ColumnName, o => o.Row);
foreach (var group in query)
{
Console.WriteLine("ColumnName: {0}", group.Key);
foreach (var item in group)
{
Console.WriteLine(item);
}
}
The downside of either approach is you're ending up with an object. Retaining the results in a strongly typed manner would require some extra work given the dynamic nature of the question.

ToTable() doesn't return distinct records?

I am using datatable to return me distinct records but somehow its not returning me distinct records
I tried like
dt.DefaultView.ToTable(true, "Id");
foreach (DataRow row in dt.Rows)
{
System.Diagnostics.Debug.Write(row["Id"]);
}
It still returns me all the records. What could be wrong here?
UPDATE
My sql is as below
select t.Update ,t.id as Id, t.name ,t.toDate,t.Age from tableA t Where t.Id = 55
union
select t.Update ,t.id as Id, t.name ,t.toDate,t.Age from tableB t Where t.Id = 55
order by Id
Its very hard to do distinct in my query as there are many columns than mentioned here.

If you use a database it would be better to use sql to return only distinct records(e.g. by using DISTINCT, GROUP BY or a window function).
If you want to filter the table in memory you could also use Linq-To-DataSet:
dt = dt.AsEnumerable()
.GroupBy(r=>r.Field<int>("Id")) // assuming that the type is `int`
.Select(g=>g.First()) // take the first row of each group arbitrarily
.CopyToData‌​Table();
Note that the power of Linq starts when you want to filter these rows or if you don't want to take the first row of each id-group arbitrarily but for example the last row(acc. to a DateTime field). Maybe you also want to order the groups or just return the first ten. No problem, just use OrderBy and Take.

The issue is that you're not grabbing the new table:
var newDt = dt.DefaultView.ToTable(true, "Id");
foreach (DataRow dr in newDt.Rows) ...
the ToTable method doesn't modify the existing table - it creates a new one.

DataView view = new DataView(table);
DataTable distinctValues = view.ToTable(true, "Id");

you are not assigning the return value to any variable, try this
DataTable dtnew = dt.DefaultView.ToTable(true, "Id");
foreach (DataRow row in dtnew.Rows)
{
System.Diagnostics.Debug.Write(row["Id"]);
}