Unable to increment Counter using linq - vb.net

Question

Hello AllSo i am trying to edit and insert rows into a datatable using linq but i am unable to increment the counter using Linq
Basically what i am trying to do is first edit or the data using Select method and assigning it to variable in my query using let and then using normal Add method to add all the rows into the dt SO my first question is can i directly add all the rows without needing the counter ?
The reason i need counter is what i am trying to do is take one element per iteration using its index for example x(1).....x(n) so for the index i need counter so for counter i created a variable outside the flow and incremented it inside our linq query but it didnt work out.....
The code i have tried
(From roww In DT.AsEnumerable() Let x=DT.AsEnumerable().Select(Function(r) CStr(r("Column1")).Substring(0,3) ).ToArray Select
DT.Clone.Rows.Add(roww.Item("Some Column"),roww.Item("Column1"),x)).CopyToDataTable
(From roww In DT.AsEnumerable() Let x=DT.AsEnumerable().Select(Function(r) CStr(r("Column1")).Substring(0,3) ).ToArray Select
DT.Clone.Rows.Add(roww.Item("Some Column"),roww.Item("Column1"),x(y+1))).CopyToDataTable
Another thing what i was looking to use Expression.Increment Method but i havent used it dont know what exactly it is and whether it can be converted to int
ANy inputs ??

Answer 1

Hello all i did the above question using this query
(From roww In DT.AsEnumerable() Select
DT.Clone.Rows.Add(roww.Item("Some other data"),roww.Item("Column1"),CStr(roww.Item("Column1")).Substring(0,4))).CopyToDataTable
But i still want to know how can i increment counter if any one knows how to do it please let me know.......Even if its in C#'s format ill learn the logic or syntax
Thank you

Answer 2

While your answer is the correct solution to your query, if you had some other type of array not dependent on your original data source, you may need to index into the array in parallel with your data source. While a For..Next would be the best way to handle this, you can emulate the same effect with LINQ using Enumerable.Range and Zip.
The Let statement is translated into a Select that carries the Let variable value along with each row. The Enumerable.Range provides a source of increasing integers you can use to index into an array.
Dim addedDT = (DT.AsEnumerable() _
.Select(Function(roww) New With { Key .x = DT.AsEnumerable.Select(Function(r) CStr(r("Column1")).Substring(0,3)).ToArray, roww }) _
.Zip(Enumerable.Range(0, DT.Rows.Count), Function(xroww, y) DT.Clone.Rows.Add(xroww.roww.Item("Some Column"),xroww.roww.Item("Column1"),xroww.x(y+1))
).CopyToDataTable
Looking at the Let translation makes it more apparent that the calculation of x occurs once per data source row and is very inefficient. Pulling the constant value out makes for a better version:
Dim x = DT.AsEnumerable.Select(Function(r) CStr(r("Column1")).Substring(0,3)).ToArray
Dim addedDT = (DT.AsEnumerable() _
.Zip(Enumerable.Range(0, DT.Rows.Count), Function(roww, y) DT.Clone.Rows.Add(roww.Item("Some Column"),roww.Item("Column1"),x(y+1))
).CopyToDataTable