How to use the function in the expression that adds a column in the data table

Question

 Dim MyTable As New DataTable
 MyTable.Columns.Add("Name")
 MyTable.Columns.Add("Age", GetType(Integer))
 MyTable.Rows.Add("Ali", 9)
 MyTable.Rows.Add("Amir", 15)
 MyTable.Rows.Add("Mansour", 18)
 MyTable.Columns.Add("isOk", GetType(Boolean), "IIF(Age>=10 And Age<=20,True,False)")

IIF(Age>=10 And Age<=20,True,False)

I want to perform function(iif) operation in a custom function.

Need this operation with function

 Dim MyTable As New DataTable
 MyTable.Columns.Add("Name")
 MyTable.Columns.Add("Age", GetType(Integer))
 MyTable.Rows.Add("Ali", 9)
 MyTable.Rows.Add("Amir", 15)
 MyTable.Rows.Add("Mansour", 18)
 MyTable.Columns.Add("isOk", GetType(Boolean), MyFunc(Age))  'Error

Function MyFunc(InAge) as Boolean
If InAge>=10 And InAge<=20 then
return true
else
Return False
End If
End Function

Answer 1

Hi @Mansour_Dalir ,

Use a For Each loop to iterate through each row in the DataTable to call the MyFunc function with the Age column value to assigne the isOk column result for each row.

        For Each row As DataRow In MyTable.Rows
            row("isOk") = MyFunc(row("Age"))
        Next

    Function MyFunc(InAge As Integer) As Boolean
        If InAge >= 10 And InAge <= 20 Then
            Return True
        Else
            Return False
        End If
    End Function

Best Regards.

Jiachen Li

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Answer 2

To use a function in an expression that adds a column to a DataTable, you can define the function using a lambda expression and then use it in the DataColumn constructor. Here's an example in VB:

Dim workTable As New DataTable("Customers")
workTable.Columns.Add("Total", GetType(Double))
workTable.Columns.Add("SalesTax", GetType(Double), "Total * 0.086")
Dim getDiscount = Function(price As Double) price * 0.1
workTable.Columns.Add("Discount", GetType(Double), "getDiscount(UnitPrice)")

In this example, we define a lambda expression getDiscount that takes a price parameter and returns price * 0.1. We then use this lambda expression in the DataColumn constructor for the "Discount" column, passing in "getDiscount(UnitPrice)" as the expression.

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References:

• Creating Expression Columns
• How to: Create a Lambda Expression (Visual Basic)