Parsing a string with match groups

[Dominick Marciano]

Let me start by saying that I'm not the greatest with Regular Expressions, but from research it seems that they are the best way to go for what I need; I just don't fully understand how to use them with matching groups. In my application I need to parse a boolean string that can have any number of parameters. The following are some examples:

Name=John or Name=Jane
Name=John or Name=Jane and Date=Now

I need to be parse any variation of these strings ('and' and 'or' are the only boolean operators that can be present) so that I get a list such as:

Name=John
or
Name=Jane
and
Date=Now

I don't need to parse the strings with the '=' sign, but I do need the 'or' & 'and' operators so when I build my query in code I know how to connect each statement to the next (ie:Name=John should be ORed with Name=Jane which should be ANDed with Date=Now) So far I have only been able to get a list such as

Name=John
Name=Jane
Date=Now

by using the following code:

Dim Pattern As String = "(\S+\x3D\S+)"

While Regex.Matches(query, Pattern).Count > 0
Dim oMatches As MatchCollection = Regex.Matches(query, Pattern)
For Each oMatch In oMatches
Dim Operand1 = oMatch.Groups(0).Value
Next
End While

but I lose the boolean operators in the process. If anyone could please help me with a regular expression so I would get the groups I have now, but with the operators in between the appropriate expressions, it would be greatly appreciated. Thanks.

[Matt T Heffron]

I'd suggest doing the matches in phases so that you can track operator presedence: and is higher presendence than or: In fact you probably don't need to use Regex, String.Split should be able to do the job: First divide the input based on 'and':

Dim andSeparators() As String = {" and "}
Dim andTerms() as String
andTerms = String.Split(andSeparators, query)

Next for each of the andTerms do a similar String.Split on " or "

[Gabriel Szabo]

You can use the alternation syntax "(a|b)". A match in your case is an expression in form "parameter=value", or an operator. Operator can be "or" or "and" and must have a space before and after. Following pattern produces the results you wanted. For an input string "Name=John or Name=Jane and Date=Now" you get matches "Name=John", " or ", "Name=Jane", " and ", "Date=Now":

"(\w+=\w+|\s(or|and)\s)"

If you want to use regex for validation only, you can do it this way (note that you get only a single match with this pattern):

Regex.IsMatch(inputStr, "^(\w+=\w+|\s(or|and)\s)+$");

And you can go even further with validation. Following pattern uses positive look ahead/behind syntax to ensure that operators are enclosed with valid expressions:

Regex.IsMatch(inputStr, "^(\w+=\w+|(?<=\w+=\w+)\s(or|and)\s(?=\w+=\w+))+$");

Gabriel Szabo