Function for minimum non-zero with multiple additional conditions

Question

This function works, but seems unnecessarily complicated. I would like to simplify but performance is vital as it is called many times.

The conditions are:

1) If either value is negative, then result is -1

2) If both values are zero, then result is zero

3) If NeedMax is true, result is largest value

4) If NeedMax is false, result is smallest non-zero value

CODE:

Public Function SelValue(ValOne As Long, ValTwo As Long, _
 Optional NeedMax As Boolean = True) As Long
 If ValOne < 0 Or ValTwo < 0 Then
 SelValue = -1
 ElseIf ValOne = 0 And ValTwo = 0 Then
 SelValue = 0
 ElseIf NeedMax Then
 If ValOne > ValTwo _
 Then SelValue = ValOne _
 Else SelValue = ValTwo
 Else
 If ValOne = 0 Then
 SelValue = ValTwo
 ElseIf ValOne > ValTwo And ValTwo <> 0 Then
 SelValue = ValTwo
 Else
 SelValue = ValOne
 End If
 End If
End Function

Can anyone suggest a more direct, and hopefully faster, approach?

• Mathieu Guindon: Are the parameters more likely to be positive or negative? It's called many times in what context?
• Rey Juna: @MathieuGuindon They should always be positive. The check for negatives is really an error check so that if SelValue is returned as -1 I can check for that. It is called to find an index number for a find result.
• Mathieu Guindon: That's a code smell. If legal values should be positive, then illegal values should throw an error (#5 "invalid procedure call or argument" seems sensible), and that way you avoid a systematic check for exceptional conditions. Seeing the function in its usage context could be helpful and valuable IMO.
• Rey Juna: There really should never be a negative value. Maybe I am being over cautious, but I always try to cover the bases.
• Mathieu Guindon: I've rolled back the last edit, since it incorporates feedback from an answer. Please don't invalidate answers with edits! =)

Answer 1

Try to use meaningful names. What's names (SelValue, ValOne,...) stands for? It don't give info on their purpose or usage.

Furthermore, you can simplify a lot your conditional branchments, using only this:

If ValOne < 0 Or ValTwo < 0 Then
 SelValue = -1
' remove this following condition to discard case 4
Else If ValOne = 0 Or ValTwo = 0 Then
 SelValue = ValOne + ValTwo 
ElseIf ValOne > ValTwo <> NeedMax Then 
 SelValue = ValTwo
Else
 SelValue = ValOne
End If

not fully tested, but should do the trick

Edit : fixed case (4), where NeedMax is false and one of values is 0.

• Rey Juna: Except when one value is negative this always returns the sum of the two values. Doesn't meet my conditions.
• Calak: @ReyJunaRey did you tested? If one value (Or both) is negative, it return -1...
• Rey Juna: Correct, if one (or both) is negative it will return -1. Otherwise it always returns the sum of the two values whereas I would like to either return the maximum or minimum non-zero.
• Calak: No, it return the sum only if at least one of value is zero. Test it please ;)
• Calak: Fixed, it should work now. this post was just "phonecrafted", and especially the line after the comment wasn't tested.

Answer 2

This is a really funky way of formatting an If statement and is totally inconsistent with the rest of the procedure (and the way most people would format it):

 If ValOne > ValTwo _
 Then SelValue = ValOne _
 Else SelValue = ValTwo

I'd rearrange that as

 If ValOne > ValTwo Then
 SelValue = ValOne 
 Else 
 SelValue = ValTwo
 End If

• AJD: SelValue = If(ValOne > ValTwo, ValOne, ValTwo). Using the VBA If() function in this context is safe because all components are values, not objects and not likely to throw error in themselves.
• Rey Juna: @AJD, I like that approach. You should post as an answer.
• Mathieu Guindon: @AJD that's IIf ;-)
• Comintern: @AJD IIf is a function, so it involves stack manipulation - i.e. copying memory, pushing the stack pointer, popping back, etc. That's a horrible idea if you're looking for raw performance.
• AJD: @MathieuGuindon: thanks - yes IIf(). If() works in .Net as well and is safer.

Answer 3

First, the default value seems like it's overkill here. The function should be a Min function or a Max function, not both. It's not going to kill you to have two functions with clear arguments that describe what they are doing.

The naming is suspect too. SelValue doesn't sound like the name of a function - it sounds like a procedure or property. It invokes the idea of doing something, not returning a value. I'd rename it. Note that I can't even suggest a good name because of the first thing, because FindHigherOrLowerOfTwoNumbers() seems a little... weird.

As far as performance, that would be the last thing on my mind. This is only performing comparison operations between numbers, and that should be blazingly fast regardless of how many extra comparisons you've managed to sneak in there:

• You don't have to check explicitly to see if they're both zero. If they're equal and both happen to be zero, you'll get zero back anyway.
• If both of them are the same, that's the only check you need to do. Just pick one and return it.

---

VBA's If statements don't short circuit, so I'd structure this as a Select Case and filter away remaining cases on my way down.

Select Case True
 Case ValOne < 0 Or ValTwo < 0
 SelValue = -1
 Case ValOne = ValTwo
 SelValue = ValOne
 Case NeedMax
 If ValOne > ValTwo Then
 SelValue = ValOne
 Else
 SelValue = ValTwo
 End If
 Case ValOne < ValTwo
 SelValue = ValOne
 Case Else
 SelValue = ValTwo
End Select

• Mathieu Guindon: Oh well, there goes my draft! :)
• Comintern: @MathieuGuindon - Reading fail. Edited (although I'll stand by the rest of that bullet).
• Mathieu Guindon: Based on the comment conversation though, it appears -1 is actually an error flag; hence I'd move that first case last, and throw error 5 - eliminating a highly redundant if-check at the call site.
• Comintern: @MathieuGuindon That would make a good answer. ;-)
• AJD: Yeah, I like the Select Case approach - I was going to add it to my answer.

Answer 4

I'm not sure the functional solution below may contribute to better performance, but it's a way of dealing with the three conditional expressions all at once.

The maximum of two numbers A and B can expressed functionally as:

(Abs(A + B) + Abs(A - B)) /2

and the minimum as:

(Abs(A + B) - Abs(A - B)) /2

Noting that the boolean value True is evaluated to -1 and False to 0, thus the expression:

- (1 + 2 * NeedMax)

is evaluated to 1 if NeedMax is True, and -1 otherwise. Combining all the three preceding expressions yields the desired solution:

Public Function SelValue(ValOne As Long, ValTwo As Long, _
 Optional NeedMax As Boolean = True) As Long
 SelValue = (Abs(ValOne + ValTwo) - (1 + 2 * NeedMax) * Abs(ValOne - ValTwo)) / 2
End Function

This returns the maximum of the two values if NeedMax is True and and the minimum otherwise. Checking wether both values are zero is redundant; the max and min would have the same value; namely Zero. Checking wether both values are negative is left (as in your comment) to the calling procedure.

• Rey Juna: This doesn't seem to work right when NeedMax is False and only one of the values is 0. It returns 0 when it should return the non-zero number (Condition 4).
• user186038: I see. I've skipped that condition. Anyway, implementing that condtion functionnaly although feasible, is not practical regarding performance. For sake of brieviety denote A and B as the numbers ValOne and ValTwo. Denote P as NeedMax and Q as the Boolean test (A>0 AND B>0) then SelValue =B + (A>B) * (B-A) + Q*(1+P)*((B-A) - 2*(A>B)*(B-A))
• Rey Juna: Hmm, seems more complex to understand than the answer and, though I'm not sure that I entered it correctly, when I try it with A=3, B=1, and P=False I get a result of 9.
• user186038: You're right as there's a typo (- operater instead of +). SelValue =B + (A>B) * (B-A) + Q*(1+P)*((B-A) + 2*(A>B)*(B-A)) . As you may see, this implicit boolean casting may not suit your sake after performance optimization.

Answer 5

This is Excel, so some Excel built-in perks can be used.

Return a Variant, not a defined type because you can then return an error quite easily. Yes this does apply to general VBA as well.

Return early from the function if you can to save further checks - although in this simple example it is not really necessary.

Every time I see an ElseIf I think that there is something in here that can be improved.

If you are looking to expand this later, then write it for such extension. The first example below just cleans up the code.

Public Function SelValue(ValOne As Long, ValTwo As Long, _
 Optional NeedMax As Boolean = True) As Variant
 If ValOne < 0 Or ValTwo < 0 Then
 SelValue = CVErr(xlErrValue)
 Exit Function
 End If
 If ValOne = 0 And ValTwo = 0 Then
 SelValue = CLng(0)
 Exit Function
 End If
 If NeedMax Then
 SelValue = IIf(ValOne > ValTwo, CLng(ValOne), CLng(ValTwo)) ' But note comments about a minor performance hit 
 Exit Function
 End If
 If ValOne = 0 Then
 SelValue = CLng(ValTwo)
 Exit Function
 End If
 ' Now that we have cleaned out the special cases above. NeedMax is False
 If ValOne > ValTwo And ValTwo <> 0 Then
 SelValue = CLng(ValTwo)
 Else
 SelValue = CLng(ValOne)
 End If
End Function

The above code is not the final way I would leave it - personally I would refactor it again because I prefer only one exit/return from a function. But the above iteration highlights something important. It isolates the logic. And you don't handle the case where ValTwo = 0

Addendum: SelValue = CVErr(xlErrValue) is only useful if the function is a UDF. Raising error #5 (Err.Raise 5) here and still returning a Long is a valid approach for a non-UDF. Thanks to Mathieu Guindon.

• AJD: I did it again! If() instead of IIf()
• Mathieu Guindon: SelValue = CVErr(xlErrValue) is only useful if the function is a UDF. I would absolutely Err.Raise 5 here and still return a Long.
• Vogel612: Returning Variant to be able to return an Error instead of Raising it is bad advice. That's even more true when seen through the lens of performance, where returning Variant incurs overhead for type-coercion and IDispatch/IUnknown.
• AJD: @Vogel612: depends on the scope of the lens. Yes, in the scope of the single function there are performance and storage/space hits, but at the wider scale, performance and functionality is improved due to the improved logic flow ("is that -1 really -1 or is it some sort of coded error result?") An optimal system requires that some or all of the sub-systems are sub-optimal.