Recursive searching a pattern in a string

Question

I am using c#. I have following string

<li> 
    <a href="abc">P1</a> 
    <ul>
        <li><a href = "bcd">P11</a></li>
        <li><a href = "bcd">P12</a></li>
        <li><a href = "bcd">P13</a></li>
        <li><a href = "bcd">P14</a></li>
    </ul>
</li>
<li> 
    <a href="abc">P2</a> 
    <ul>
        <li><a href = "bcd">P21</a></li>
        <li><a href = "bcd">P22</a></li>
        <li><a href = "bcd">P23</a></li>
    </ul>
</li>
<li> 
    <a href="abc">P3</a> 
    <ul>
        <li><a href = "bcd">P31</a></li>
        <li><a href = "bcd">P32</a></li>
        <li><a href = "bcd">P33</a></li>
        <li><a href = "bcd">P34</a></li>
    </ul>
</li>
<li> 
    <a href="abc">P4</a> 
    <ul>
        <li><a href = "bcd">P41</a></li>
        <li><a href = "bcd">P42</a></li>
    </ul>
</li>

My aim is to fill the following list from the above string.

List<class1>

class1 has two properties,

string parent;
List<string> children;

It should fill P1 in parent and P11,P12,P13,P14 in children, and make a list of them.

Any suggestion will be helpful.

Edit

Sample

public List<class1> getElements()
{
    List<class1> temp = new List<class1>();
    foreach(// <a> element in string)
    {
        //in the recursive loop
        List<string> str = new List<string>();
        str.add("P11");
        str.add("P12");
        str.add("P13");
        str.add("P14");

        class1 obj = new class1("P1",str);
        temp.add(obj);
    }
    return temp;
}

the values are hard coded here, but it would be dynamic.

@lazyberezovsky : If we are searching in string having <li> inside <li>, then it would be recursive — RTRokzzz
– RTRokzzz, Commented Nov 30, 2012 at 13:23
You can download Html Agility Pack from nuget, it will add a dll to your project as a reference, there is plenty of documentation out there — CR41G14
– CR41G14, Commented Nov 30, 2012 at 13:24

slebetman · Accepted Answer · 2012-11-30 14:05:03Z

4

What you want is a recursive descent parser. All the other suggestions of using libraries are basically suggesting that you use a recursive descent parser for HTML or XML that has been written by others.

The basic structure of a recursive descent parser is to do a linear search of a list of tokens (in your case a string) and upon encountering a token that delimits a sub entity call the parser again to process the sublist of tokens (substring).

You can Google for the term "recursive descent parser" and find plenty of useful result. Even the Wikipedia article is fairly good in this case and includes an example of a recursive descent parser in C.

answered Nov 30, 2012 at 14:05

slebetman

115k19 gold badges147 silver badges180 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Tim Schmelter · Accepted Answer · 2012-11-30 14:29:47Z

3

If you can't use a third party tool like my recommended Html Agility Pack you could use the Webbrowser class and the HtmlDocument class to parse the HTML:

WebBrowser wbc = new WebBrowser();
wbc.DocumentText = "foo"; // necessary to create the document
HtmlDocument doc = wbc.Document.OpenNew(true);
doc.Write((string)html); // insert your html-string here
List<class1> elements = wbc.Document.GetElementsByTagName("li").Cast<HtmlElement>()
    .Where(li => li.Children.Count == 2)
    .Select(outerLi => new class1
    {
        parent = outerLi.FirstChild.InnerText,
        children = outerLi.Children.Cast<HtmlElement>()
            .Last().Children.Cast<HtmlElement>()
            .Select(innerLi => innerLi.FirstChild.InnerText).ToList()
    }).ToList();

Here's the result in the debugger window:

enter image description here

edited Nov 30, 2012 at 14:29

answered Nov 30, 2012 at 14:07

Tim Schmelter

462k79 gold badges719 silver badges980 bronze badges

2 Comments

RTRokzzz Over a year ago

I tried your code, but unfortunately it is showing following error ActiveX control '8856f961-340a-11d0-a96b-00c04fd705a2' cannot be instantiated because the current thread is not in a single-threaded apartment.

Tim Schmelter Over a year ago

@user1866361: Is this a console application? It seems that this will solve the problem: stackoverflow.com/q/5519294/284240 Webbrowser is a Winforms class.

Arie · Accepted Answer · 2012-11-30 14:27:16Z

1

You can also use XmlDocument:

XmlDocument doc = new XmlDocument();
doc.LoadXml(yourInputString);
XmlNodeList colNodes = xmlSource.SelectNodes("li");
foreach (XmlNode node in colNodes)
{
    // ... your logic here
    // for example
    // string parentName = node.SelectSingleNode("a").InnerText;
    // string parentHref = node.SelectSingleNode("a").Attribures["href"].Value;
    // XmlNodeList children = 
    //       node.SelectSingleNode("ul").SelectNodes("li");
    // foreach (XmlNode child in children)
    // {
    //         ......
    // }
}

answered Nov 30, 2012 at 14:27

Arie

5,4033 gold badges37 silver badges57 bronze badges

Collectives™ on Stack Overflow

Recursive searching a pattern in a string

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related