在VB.net中实现类似于EXCEL查找的功能

Question

I have a lot of code that requires random numbers to be generated and then options selected based on percentage. I have it working without issue by simply using an implementation of the Mersenne Twister and generating a double between 0 and 100, then assigning results by percentage with select case. It works fine, but it's very cumbersome and truth be told, I'm tired of continuously writing this out everytime.

I'd much prefer something similar to EXCEL's Lookup Function where you give two arrays such as LOOKUP(5, {1,10,20,30,40}, {"1-10", "11-20", "21-30","31-40"})

Which in this case would return: "1-10" since 5 is between 1-10.

Is there an easy way to implement a C#/VB.Net version of this using LINQ? I'm sure there must be but I'm at a loss for how to implement something like this. It would be far easier to write this one line of code than long select case statements.

If there is a better way than implementing an equivalent of an EXCEL lookup function, I'd love to know that as well...

Answer 1

I am assuming your are doing the second form of lookup, as the first would throw an error if the first argument doesn't exactly match an element in the array passed in the second argument.

This should work:

Public Function LookUp(Of T)(ByVal value As IComparable, ByVal Values() As IComparable, ByVal Result() As T) As Object
    If Values Is Nothing Then Throw New ArgumentException("Values cannot be nothing")
    If Values.Length = 0 Then Throw New ArgumentException("Values can not be empty")
    If Result Is Nothing Then Throw New ArgumentException("Result cannot be nothing")
    If Values.Length = 0 Then Throw New ArgumentException("Result can not be empty")
    If Values.Length <> Result.Length Then Throw New ArgumentException("Values and Result must have the same length")
    Dim i As Integer = 0
    While i < Values.Length AndAlso value.CompareTo(Values(i)) < 0
        i += 1
    End While
    if i = Values.Length Then i-=1
    Return Result(i)
End Function

Usage:

Dim Result as string = LOOKUP(5, {1,10,20,30,40}, {"1-10", "11-20", "21-30","31-40"})

Answer 2

There are few ways to do it with LINQ or Array/List .FindIndex, but integer division is probably the best:

Dim d = 10.1, a = {1, 10, 20, 30, 40}, b = {"1-10", "11-20", "21-30", "31-40"}

Dim s1 = b(a.Count(Function(i) i <= d) - 1)

Dim s2 = b(Array.FindLastIndex(a, Function(i) i <= d))

Dim s3 = $"{d - d Mod 10 + 1}-{d - d Mod 10 + 10}"      ' "11-20"

Answer 3

I actually came up with something similar to @Alexander Higgins answer on my own after I sat there and thought about it for a few minutes. I call it like so:

CaseLookup({41, 59, 80, 101}, {"Balanced", "PowerBack", "Receiving", "OneCut"}, 0, 100) 

Basically I set the boundary for the next item and loop to find the first index it is less than, which means it would fall within that range. I then simply take the same index from the lookup array as the value.

Public Shared Function CaseLookup(numArray As Array, lookupArray As Array, minVal As Double, maxval As Double) As String
        Dim result As String = ""
        Dim GetNum As Double = MT.GenerateDouble(minVal, maxval)

        If numArray.Length <> lookupArray.Length Then 'Checks to make sure the arrays are the same length
           Throw New Exception("numArray and lookupArray MUST be the same length!")
           Exit Function
        End If

        For i = 0 To numArray.Length - 1
            If GetNum < numArray(i) Then result = lookupArray(i).ToString()
        Next i
        Return result
    End Function