Linq to XML in visual basic

Question

I'm wondering if its legal to add a static regex statement in the select statement of a linq query. Also is there an example and what the syntax for doing it?

To strip <a> tags from HTML and return just a portion of the tag to my Generic.IEnumerable(Of String) list.


Dim links = From link In Mytabledata...<a> _
                     Where InStr(link.@href, "[AC35]") > 0 _
                      Select ( get text between "code =" and "&" in a regex static statement from link.value)


I could only find a couple of examples of comparing matches. None of using static regex calls to format the returned list in line. Can you only use matches?

The one thing that I did find why searching around was a regex to linq project by the guy who wrote Regulator.

http://weblogs.asp.net/rosherove/archive/2008/05/06/introducing-linq-to-regex.aspx

Answer 1

Does it have to be a static Match call? Here is an example with a Match call on a Regex instance:

Code Snippet

        Dim pattern As New Regex("code=([^&]*?)&")
        Dim example As XElement = _
        <root>
            <a>foo code=bar&amp;whatever=baz</a>
        </root>
        Dim query As IEnumerable(Of String) = _
        From a In example...<a> _
        Select pattern.Match(a.Value).Groups()(1).Value

        For Each s As String In query
            Console.WriteLine(s)
        Next

 

 

If you really want a static call:

Code Snippet

        Dim pattern As String = "code=([^&]*?)&"
        Dim example As XElement = _
        <root>
            <a>foo code=bar&amp;whatever=baz</a>
        </root>
        Dim query As IEnumerable(Of String) = _
        From a In example...<a> _
        Select Regex.Match(a.Value, pattern).Groups()(1).Value

        For Each s As String In query
            Console.WriteLine(s)
        Next

 

The first example should be more efficient.

 

If the sample does not help then please provide your sample XML you want to process.

Answer 2

Thank you very much, those are two great examples. The only problem I have now is how to change the Select so that if there is no match, do not to put a empty string into the resulting list. Just duplicated the Select in the Where clause for the moment, but there should be a more elegant way to only select if there is a positive result of the regex.


Your example was far more readable and understandable than the Microsoft one at:

http://msdn.microsoft.com/en-us/library/bb882639.aspx

Answer 3

You can use a Let clause to store the Match result and then check Success in the Where clause:

Code Snippet

        Dim pattern As New Regex("code=([^&]*?)&")
        Dim example As XElement = _
        <root>
            <a>foobar</a>
            <a>foo code=bar&amp;whatever=baz</a>
            <a>bar code=foo&amp;baz=whatever</a>
        </root>
        Dim query As IEnumerable(Of String) = _
        From a In example...<a> _
        Let m = pattern.Match(a.Value) _
        Where m.Success _
        Select m.Groups()(1).Value

        For Each s As String In query
            Console.WriteLine(s)
        Next

 

 

Answer 4

Thanks thats exactly what I was looking for.