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How to get a column value from data table with Linq

How to get a column value from a data table object. I have the id column on which basis I am trying to get another column value.
e.g. ApplicationId is the primary key column which I have and now I want to get the xyz column value for this ApplicationId.

I have accomplished my result by making use of the following Linq statement
List<string> lstResult= (from table in dt.AsEnumerable()
where table.Field<int>("Id") == id
select table.Field<string>("status")).ToList();
string dtStatus = lstResult[0];

you can do it lik this
var results = (from rows in dt.AsEnumerable() select new {resultcolumnname=row["resultcolumnname"]}).where(item=>item.columnname == value).ToList()

var x= from myrow in myDataTable.asEnumerable() where myrow.ApplicationId==[YourValue] select myRow.[ColumnYouWant];
I am not great when it comes to linq but this should do the trick.

Group by one column and Distinct by another column using Linq

I am using a Linq query to groupBy a column name and return a list of rows.
var query = from row in ProcessSummaryData.AsEnumerable()
group row by new { Key = row .Field<string>("GroupDescription") } into g
select new
{
GroupDescription = g.Key,
Values = g.ToList(),
};
The output of this query is something like this
GroupDescription Values
1 12,abc,xyz
12,abx,yut
13,tye,lki
2 14,asd,acd
Now the in the above example Values is a DataRow and I have just given an example of values in it.
Now what I want is that for GroupDescription '1' the output only has one row with '12' value.
I have tried a few things one of which is to have another Linq query on first list but that's over complicating things.
How do I use linq to group by first column and then use Distinct on certain column returned list to get only Distinct rows?

To get the first occurrence of a field's values you can group by that field and then take the first row of each grouping.
var query = from row in ProcessSummaryData.AsEnumerable()
group row by new { Key = row .Field<string>("GroupDescription") } into g
select new
{
GroupDescription = g.Key,
Values = (from value in g.ToList()
group value by value["Id"] into valueGroup
select valueGroup.First()).ToList()
};

Merging 2 datatables in to 1 datatable with same number of rows.

How can i merge two Datatables into the same row. I am using different stored procedures to get data into datasets. In asp.net using c#, i want to merge them so there are same number of rows as table 1 with an added column from table 2.
For example:
DataTable table1 = dsnew.Tables[0];
DataTable table2 = dsSpotsLeft.Tables[0];
table1.Merge(table2);
This is fetching me 4 rows instead of 2 rows. What am i missing here? Thanks in advance!!

You cannot use the method Merge in this case, instead you should create new DataTable dt3, and then add columns and rows based on the table 1 and 2:
var dt3 = new DataTable();
var columns = dt1.Columns.Cast<DataColumn>()
.Concat(dt2.Columns.Cast<DataColumn>());
foreach (var column in columns)
{
dt3.Columns.Add(column.ColumnName, column.DataType);
}
//TODO Check if dt2 has more rows than dt1...
for (int i = 0; i < dt1.Rows.Count; i++)
{
var row = dt3.NewRow();
row.ItemArray = dt1.Rows[i].ItemArray
.Concat(dt2.Rows[i].ItemArray).ToArray();
dt3.Rows.Add(row);
}

Without knowing more about the design of these tables, some of this is speculation.
What it sounds like you want to perform is a JOIN. For example, if you have one table that looks like:
StateId, StateName
and another table that looks like
EmployeeId, EmployeeName, StateId
and you want to end up with a result set that looks like
EmployeeId, EmployeeName, StateId, StateName
You would perform the following query:
SELECT Employee.EmployeeId, Employee.EmployeeName, Employee.StateId, State.StateName
FROM Employee
INNER JOIN State ON Employee.StateId = State.StateId
This gives you a resultset but doesn't update any data. Again, speculating on your dataset, I'm assuming that your version of the Employee table might look like the resultset:
EmployeeId, EmployeeName, StateId, StateName
but with StateName in need of being populated. In this case, you could write the query:
UPDATE Employee
SET Employee.StateName = State.StateName
FROM Employee
INNER JOIN State ON Employee.StateId = State.StateId
Tested in SQL Server.

Assuming you have table Category and Product related by CategoryID, then try this
var joined = from p in prod.AsEnumerable()
join c in categ.AsEnumerable()
on p["categid"] equals c["categid"]
select new
{
ProductName = p["prodname"],
Category = c["name"]
};
var myjoined = joined.ToList();
Sources
LINQ query on a DataTable
Inner join of DataTables in C#
http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataset/thread/ecb6a83d-b9b0-4e64-8107-1ca8757fe58c/
That was a LINQ solution. You can also loop through the first datatable and add columns from the second datatable

C# Linq filter DataTable using array elements

I want filter the data in a data table using linq.
My scenario is I have an array of elements which contains dates created dynamically and in the data table we have columns as id,date,etc.
We have to retrieve the id's which contains all the dates in array
ex:
string[] arr={"10/10/2012","11/11/2012","9/9/2012"}
Table :
ID date
1 10/10/2012
2 11/11/2012
1 9/9/2012
6 9/9/2012
3 9/9/2012
6 11/11/2012
1 11/11/2012
Output would be 1 - because only id '1' has all the array elements.
To accomplish above functionality I am using the Linq query shown below. But I am literally failing.
Dim volunteers As DataTable =
(From leftTable In dtavailableVolunteers.AsEnumerable()
Join rightTable In dtavailableVolunteers.AsEnumerable()
On leftTable.VolunteerId Equals rightTable.VolunteerId
Where SelectedDatesArray.All(Function(i) rightTable.Field(Of String)("SelectedDate").Equals(i.ToString()))
Select rightTable).CopyToDataTable()

Lets say your datatable is dt
DataRow[] dr = dt.Select("date in (" + string.join("," , arr) + ")");
string[] st = dr.Select(ss => ss["id"].ToString()).ToArray();
OR
DataTable newdt = dr.CopyToDataTable();
Second line is of LINQ

You could group the rows by ID, and then find the groups where: there does not exist an arr element which the group's dates doesn't contain that element. I mean something like:
var result = from item in list
group item by item.ID into grouping
where !arr.Exists(date =>
!grouping.Select(x => x.Date).Contains(date))
select grouping.Key;

Here is another version:
from volunteer in dtavailableVolunteers
group volunteer by volunteer.Id into g
let volunteerDates = g.Select(groupedElement=>groupedElement.date)
where arr.All(date=>volunteerDates.Contains(date))
select g.Key

LINQ TO DataSet: Multiple group by on a data table

I am using Linq to dataset to query a datatable. If i want to perform a group by on "Column1" on data table, I use following query
var groupQuery = from table in MyTable.AsEnumerable()
group table by table["Column1"] into groupedTable
select new
{
x = groupedTable.Key,
y = groupedTable.Count()
}
Now I want to perform group by on two columns "Coulmn1" and "Column2". Can anybody tell me the syntax or provide me a link explaining multiple group by on a data table??
Thanks

You should create an anonymous type to do a group by multiple columns:
var groupQuery = from table in MyTable.AsEnumerable()
group table by new { column1 = table["Column1"], column2 = table["Column2"] }
into groupedTable
select new
{
x = groupedTable.Key, // Each Key contains column1 and column2
y = groupedTable.Count()
}