Quick and Easy Currency Extractor

by Chris Love

I have fallen in love with Regular Expressions over the past few months. Over the weekend I replaced some moderately complicated parsing code in an older application with a Regular Expression and found another quick use for one this morning, extracting a currency value.

So here was my problem, I have an application that displays the cost of an item in several ways, the common $##.## or $##.##/[time frame] and so on. I needed to just grab the actual amount to store in my database. A few years ago I would have thought ‘Oh great here go 4-5 hours of my life’. Not anymore today I spent 5 minutes thinking about and testing a simple pattern to extract just the dollar amount.

Potential Text to Extract From

Oranges $4.99/lb
Milk $2.69/quart
Rent $1000/month
Honda Accord $21,000.00

    
Public
Function
 ExtractDollarAmount(ByVal
 sDollar As
String
) As
Double
 
        
Dim
 r As
New
 Regex("(\d+\.{1}\d{1,2})"
)
 
        
For
Each
 m As
 Match In
 r.Matches(sDollar)
            
Try
                
Return
 Convert.ToDouble(m.Value)
            
Catch
 ex As
 FormatException
                
'Return -1D
                
Throw
            
Catch
 exo As
 OverflowException
                
'Return -2D
                
Throw
            
End
Try
 
        
Next
 
    
End
Function

C#:

        
public
double
 ExtractDollarAmount(string
 sDollar)
        {
            
Regex
 r = new
Regex
("(\\d+\\.{1}\\d{1,2})"
);
            
foreach
 (Match
 m in
 r.Matches(sDollar))
            {
                
try
                {
                    
return
Convert
.ToDouble(m.Value);
                }
                
catch
 (FormatException
 ex)
                {
                    
throw
;
                }
                
catch
 (OverflowException
 exo)
                {
                    
throw
;
                }
            }
            
return
 -1D;
        }

This method is real simple as well as the expression. It does have some faults, but like I said it was 5 minutes of time, but solved a fairly common need I think many of us have. I added this method to the base Page class of this application, but will most likely place it some sort of utility class as I complete abstracting my core framework.
If you have any suggestions on making this a stronger pattern, please feel free to let me know. I am going to see about posting this on RegExLib.com later today.