Rounding in MS Access

Question

Whats the best way to round in VBA Access?

My current method utilizes the Excel method

Excel.WorksheetFunction.Round(...

But I am l

Answer 1

Unfortunately, the native functions of VBA that can perform rounding are either missing, limited, inaccurate, or buggy, and each addresses only a single rounding method. The upside is that they are fast, and that may in some situations be important.

However, often precision is mandatory, and with the speed of computers today, a little slower processing will hardly be noticed, indeed not for processing of single values. All the functions at the links below run at about 1 µs.

The complete set of functions - for all common rounding methods, all data types of VBA, for any value, and not returning unexpected values - can be found here:

Rounding values up, down, by 4/5, or to significant figures (EE)

or here:

Rounding values up, down, by 4/5, or to significant figures (CodePlex)

Code only at GitHub:

VBA.Round

They cover the normal rounding methods:

• Round down, with the option to round negative values towards zero

• Round up, with the option to round negative values away from zero

• Round by 4/5, either away from zero or to even (Banker's Rounding)

• Round to a count of significant figures

The first three functions accept all the numeric data types, while the last exists in three varieties - for Currency, Decimal, and Double respectively.

They all accept a specified count of decimals - including a negative count which will round to tens, hundreds, etc. Those with Variant as return type will return Null for incomprehensible input

A test module for test and validating is included as well.

An example is here - for the common 4/5 rounding. Please study the in-line comments for the subtle details and the way CDec is used to avoid bit errors.

' Common constants.
'
Public Const Base10     As Double = 10

' Rounds Value by 4/5 with count of decimals as specified with parameter NumDigitsAfterDecimals.
'
' Rounds to integer if NumDigitsAfterDecimals is zero.
'
' Rounds correctly Value until max/min value limited by a Scaling of 10
' raised to the power of (the number of decimals).
'
' Uses CDec() for correcting bit errors of reals.
'
' Execution time is about 1µs.
'
Public Function RoundMid( _
    ByVal Value As Variant, _
    Optional ByVal NumDigitsAfterDecimals As Long, _
    Optional ByVal MidwayRoundingToEven As Boolean) _
    As Variant

    Dim Scaling     As Variant
    Dim Half        As Variant
    Dim ScaledValue As Variant
    Dim ReturnValue As Variant

    ' Only round if Value is numeric and ReturnValue can be different from zero.
    If Not IsNumeric(Value) Then
        ' Nothing to do.
        ReturnValue = Null
    ElseIf Value = 0 Then
        ' Nothing to round.
        ' Return Value as is.
        ReturnValue = Value
    Else
        Scaling = CDec(Base10 ^ NumDigitsAfterDecimals)

        If Scaling = 0 Then
            ' A very large value for Digits has minimized scaling.
            ' Return Value as is.
            ReturnValue = Value
        ElseIf MidwayRoundingToEven Then
            ' Banker's rounding.
            If Scaling = 1 Then
                ReturnValue = Round(Value)
            Else
                ' First try with conversion to Decimal to avoid bit errors for some reals like 32.675.
                ' Very large values for NumDigitsAfterDecimals can cause an out-of-range error 
                ' when dividing.
                On Error Resume Next
                ScaledValue = Round(CDec(Value) * Scaling)
                ReturnValue = ScaledValue / Scaling
                If Err.Number <> 0 Then
                    ' Decimal overflow.
                    ' Round Value without conversion to Decimal.
                    ReturnValue = Round(Value * Scaling) / Scaling
                End If
            End If
        Else
            ' Standard 4/5 rounding.
            ' Very large values for NumDigitsAfterDecimals can cause an out-of-range error 
            ' when dividing.
            On Error Resume Next
            Half = CDec(0.5)
            If Value > 0 Then
                ScaledValue = Int(CDec(Value) * Scaling + Half)
            Else
                ScaledValue = -Int(-CDec(Value) * Scaling + Half)
            End If
            ReturnValue = ScaledValue / Scaling
            If Err.Number <> 0 Then
                ' Decimal overflow.
                ' Round Value without conversion to Decimal.
                Half = CDbl(0.5)
                If Value > 0 Then
                    ScaledValue = Int(Value * Scaling + Half)
                Else
                    ScaledValue = -Int(-Value * Scaling + Half)
                End If
                ReturnValue = ScaledValue / Scaling
            End If
        End If
        If Err.Number <> 0 Then
            ' Rounding failed because values are near one of the boundaries of type Double.
            ' Return value as is.
            ReturnValue = Value
        End If
    End If

    RoundMid = ReturnValue

End Function