Question 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...

 

[JohnH]

If you're happy with "." as decimal separator then for example this:

pattern = "((?<num>\d+)/(?<den>\d+))|(?<dec>\d+\.?\d+)"

Then if m.Groups("num").Success get

value = CInt(m.Groups("num").Value) / CInt(m.Groups("den").Value)

Else get

value = CDbl(m.Groups("dec").Value)

According to Wiki percentage is also a fraction, so you could include that too.

 

[tim8w]

JohnH,
Got it to run a little, but it only worked for patterns like "1/2", "3/4" but not for "1 1/2", "1 3/4" or "3.14"...

Here's what I coded:

Dim dOrigValue As Double
Dim sPattern As String = "((?<num>\d+)/(?<den>\d+))|(?<dec>\d+\.?\d+)"
Dim regExp As System.Text.RegularExpressions.Regex = New System.Text.RegularExpressions.Regex(sPattern, RegexOptions.Compiled)
Dim m As Match = regExp.Match(dgvc.Value)

If m.Success Then
dOrigValue = CInt(m.Groups("num").Value) / CInt(m.Groups("den").Value)
Else
dOrigValue = CDbl(m.Groups("dec").Value)
End If

 

[JohnH]

Surely the 'dec' pattern fits the "3.14" string I think you should be able to expand the fraction side of the expression to include mixed number fractions given what you now know.

 

[tim8w]

JohnH,
The 'dec' pattern may fit the pattern, but how do I know which part of the pattern it matched? If I just ask m.Success I don't know which part was successful...

 

[JohnH]

which part of the pattern it matched?

I talked about that in the first reply.

 

[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

 

[JohnH]

I'd rather use a single combined expression and check the group success as I explained first.
About the mixed/single fraction you could make one of the parts option y'know.
This is a great site to learn regex IMO: Regular-Expressions.info - Regex Tutorial, Examples and Reference - Regexp Patterns