RegularExpression to convert from Fraction to decimal

[Tim8w]

I need a RegularExpression that can convert a string from a fraction or decimal like "1/2" or "0.5" to a decimal "0.5". It needs to handle both cases. Input can be either fractional or decimal, output must be decimal...

 

[MrDataGuy]

May I suggest doing a series of replace statments.

Lion Crest Software Services
Anthony L. Testi
President

http://www.LionCrestSoftwareServices.com

 

[DaveInIowa]

My initial reaction was that regular expressions were overkill for this, but I could see where they could be useful in checking for a valid string format:

    Public Function ConvertDecimalOrFractionString(ByVal s As String, ByRef value As Decimal) As Boolean
        Dim result As Boolean = True

        If (Regex.IsMatch(s, "\d+\.\d+")) Then 'Parameter has a decimal point
            result = Decimal.TryParse(s, value)
        ElseIf (Regex.IsMatch(s, "\d+/\d+")) Then 'Parameter is a fraction
            Dim ixOp As Integer = s.IndexOf("/")
            Dim numerator As Integer = Convert.ToInt32(s.Substring(0, ixOp))
            Dim denominator As Integer = Convert.ToInt32(s.Substring(ixOp + 1, s.Length - ixOp - 1))
            If (denominator <> 0) Then
                value = Convert.ToDecimal(numerator / denominator)
            Else
                result = False
            End If
        End If

        Return result
    End Function

 

[DaveInIowa]

Improved version. Plus the modified regular expression makes the leading zero optional for the decimal format:

        If (Regex.IsMatch(s, "\d*\.\d+")) Then 'Parameter has a decimal point
            result = Decimal.TryParse(s, value)
        ElseIf (Regex.IsMatch(s, "\d+/\d+")) Then 'Parameter is a fraction
            Dim numer As Integer
            Dim denom As Integer
            Dim digits() As String = s.Split("/")
            result = (Integer.TryParse(digits(0), numer) AndAlso Integer.TryParse(digits(1), denom) AndAlso denom > 0)
            If (result = True) Then value = Convert.ToDecimal(numer / denom)
        End If

 

[Tim8w]

Now only missing the case for "1 3/4" and "2" (No decimal)

 

[strongm]

Add a reference to the COM library Microsoft Script Control. Then cheat ...

[blue]    Private Function Fraction(ByVal strSource As String) As String
        Dim sc As New MSScriptControl.ScriptControl()
        Dim RunningTotal As Double
        Dim Component As String

        sc.Language = "VBScript"

        For Each Component In Split(TextBox1.Text, " ")
            RunningTotal = RunningTotal + sc.Eval(Component)
        Next

        Fraction = RunningTotal.ToString

    End Function[/blue]

 

[Tim8w]

I ended up using four different RegEx to catch all the cases:

sPattern = "((?<whole>\d+) (?<num>\d+)/(?<den>\d+))"    ' 1 1/2 case
regExp = New System.Text.RegularExpressions.Regex(sPattern, RegexOptions.Compiled)
m = regExp.Match(dgvc.Value)

If m.Success Then
    dDecValue = CInt(m.Groups("whole").Value) + CInt(m.Groups("num").Value) / CInt(m.Groups("den").Value)
Else
    sPattern = "((?<num>\d+)/(?<den>\d+))"              ' 3/4 case
    regExp = New System.Text.RegularExpressions.Regex(sPattern, RegexOptions.Compiled)
    m = regExp.Match(dgvc.Value)
    If m.Success Then
        dDecValue = CInt(m.Groups("num").Value) / CInt(m.Groups("den").Value)
    Else
        sPattern = "(?<dec>\d+\.?\d+)"                  ' 0.5 case
        regExp = New System.Text.RegularExpressions.Regex(sPattern, RegexOptions.Compiled)
        m = regExp.Match(dgvc.Value)
        If m.Success Then
            dDecValue = CDbl(m.Groups("dec").Value)
        Else
            sPattern = "(?<whole>\d+)"                  ' 2 case
            regExp = New System.Text.RegularExpressions.Regex(sPattern, RegexOptions.Compiled)
            m = regExp.Match(dgvc.Value)
            If m.Success Then
                dDecValue = CDbl(m.Groups("whole").Value)
            Else
                MsgBox("Error in value")
            End If
        End If
    End If
End If