Binary Searching in a List and Referring to a Specific Column of the List - vb.net

Question

I have some two column data that I read from a file and put into a list then sort alphabetically.
//The file
Hummus,0.75
Chili,0.50
Tabouli,1.25
Tzatziki,0.50
//Declaring the variables and public properties
Dim extraList As List(Of extra)
Public Class extra
Implements IComparable(Of extra)
Public Property Name As String
Public Property Price As Decimal
'Public Property extraList As List(Of extra)
Public Function CompareTo(other As extra) As Integer Implements IComparable(Of extra).CompareTo
Return Me.Name.CompareTo(other.Name)
End Function
End Class
//Puts the data into a list and sorts it
Sub Get_Extras_List()
'Reads the extras file and puts the information into a list, splitting the name of the extra and the price into separate columns
Dim allExtras = From line In System.IO.File.ReadLines("C:\Users\ExtrasList.txt")
Let Columns = line.Split(","c)
Where Columns.Length = 2
Let Price = Decimal.Parse(Columns(1).Trim())
Let Name = Columns(0).Trim()
Select New extra With {.Name = Name, .Price = Price}
extraList = allExtras.ToList()
'Sort the list alphabetically
extraList.Sort()
End Sub
Now I need to code a method that allows the user to type in an extra and search for it using a binary search to see if it exists. So far I have tried this but it just doesn't work and even if it did how do I get it to return a true or false value? (If it exists or not?)
Sub Search_Extras_List()
Dim strSearchExtra As String = Console.ReadLine()
Console.WriteLine(vbLf & "BinarySearch for '{0}':", strSearchExtra)
Dim index As Integer =
List(Of extra).BinarySearch(extraList.Name, strSearchExtra)
End Sub
Finally I have to get the user to choose one of the extras and then add the price of it to the total price. How do I refer to the price? extraList.Price? extra.Price? etc.

Answer 1

If you want to do a binary search like that, you will need to write a comparer.
Referring to List(Of T).BinarySearch Method (T, IComparer(Of T)), it could be
Public Class ExtraComparer
Implements IComparer(Of extra)
Public Function Compare(ByVal x As extra, ByVal y As extra) As Integer Implements IComparer(Of extra).Compare
If x Is Nothing Then
If y Is Nothing Then
' If x is Nothing and y is Nothing, they're equal.
Return 0
Else
' If x is Nothing and y is not Nothing, y is greater.
Return -1
End If
Else
' If x is not Nothing...
If y Is Nothing Then
' ...and y is Nothing, x is greater.
Return 1
Else
' ...and y is not Nothing, compare the names of the two extras.
'
Return x.Name.CompareTo(y.Name)
End If
End If
End Function
End Class
Which you can test with
' Get some item from the data so we know it is present...
Dim a = extraList(2).Name
Dim lookFor As New extra With {.Name = a}
Dim idx = extraList.BinarySearch(lookFor, New ExtraComparer)
Console.WriteLine($"Index of {a} is {idx}.")
(although you would probably want to do a case-insensitive string comparison).
If the index returned is negative then the item was not found. (See the documentation linked to above for more details.)
However, you might find it easier to use LINQ:
Dim a = extraList(2).Name
Dim chosenExtra = extraList.FirstOrDefault(Function(x) x.Name.Equals(a, StringComparison.CurrentCultureIgnoreCase))
If chosenExtra IsNot Nothing Then
Console.WriteLine($"User chose {chosenExtra.Name} at a price of {chosenExtra.Price}")
Else
Console.WriteLine($"User's choice of ""{a}"" was not found.")
End If
I used a case-insensitive comparison in there.
Or Just present the user with a dropdown of the available extras so that they don't have to type it.