I am trying to assign the result of the below query using the Assign activity and it is giving me the error.
I am assigning the value to a DataTable variable.
Query: InterswitchMerged_DT_SheetWithCountMO2.AsEnumerable().GroupBy(Function(i) i.Field(Of String)(“Merchant_Account_Nr”)).Where(Function(g) g.Count() >= 1).Select(Function(g) g.First).CopyToDataTable
Error: Unable to cast object of type ‘System.Double’ to type ‘System.String’.
Please note that I am using this expression before now and it is working fine.
Hi @Bukola
Welcome to our UiPath Forum! 
Could it be that you are running this query on a different DataTable than originally?
DataTable stores values according to a certain data type per column. You can check the data type of your column with the .GetType.ToString method on that column.
If I were to guess, you should explicitly cast your String value to a Double before performing comparisons on it.
@Bukola If you’re Still facing problems with that Query, Try replacing i.Field(Of String)(“Merchant_Account_Nr”) with i(“Merchant_Account_Nr”).ToString and check if it works.
My bad, you’re right -> it fails at conversion to String 
@loginerror I guess another method would be your way to use (Of Double) instead (Of String) 
But normally we wouldn’t know the Datatypes of each column and hence converting an Object to String is the method i follow