Regular Expression in CS: data extraction

Question

I have data like this:

<td><a href="/New_York_City" title="New York City">New York</a></td>

And I would like to get New York out of it.

I don't have any skill in regex what so ever. I have tried this though:

StreamReader sr = new StreamReader("c:\\USAcityfile2.txt");
string pattern = "<td>.*</td>";
Regex r = new Regex(pattern, RegexOptions.IgnoreCase);
Regex r1 = new Regex("<a .*>.*</a>", RegexOptions.IgnoreCase);
 string read = "";
while ((read = sr.ReadLine()) != null)
{
    foreach (Match m in r.Matches(read))
    {
        foreach (Match m1 in r1.Matches(m.Value.ToString()))
            Console.WriteLine(m1.Value);
    }
}
sr.Close();
sr.Dispose();

this gave me <a href="/New_York_City" title="New York City">New York</a>.

How can reach to data between <a .*> and </a>? thanks.

Answer 1

If you insist on a regex for this particular case, then try this:

String pattern = @"(?<=<a[^>]*>).*?(?=</a>)

(?<=<a[^>]*>) is a positive lookbehind assertion to ensure that there is <a[^>]*> before the wanted pattern.

(?=</a>) is a positive lookahead assertion to ensure that there is </a> after the pattern

.*? is a lazy quantifier, matching as less as possible till the first </a>

A good reference for regular expressions is regular-expressions.info

Their lookaround explanation

Answer 2

Only one Regex will do:

string pattern = "<a[^>]*>(.*)</a>";

Answer 3

           foreach (Match m1 in r1.Matches(m.Value.ToString()))
                {
                    //Console.WriteLine(m1.Value);
                    string[] res = m1.Value.Split(new char[] {'>','<'});
                    Console.WriteLine(res[2]);
                }

Did the trick, for this particular example. Still not what I am looking.

Answer 4

var g = Regex.Match(s, @"\<a[^>]+\>([^<]*)").Groups[1];

To find all values of <a> in your file you may use the following (easier) code:

        var allValuesOfAnchorTag =
            from line in File.ReadLines(filename)
            from match in Regex.Matches(line, @"\<a[^>]+\>([^<]*)").OfType<Match>()
            let @group = match.Groups[1]
            where @group.Success
            select @group.Value;

However you seem to work with XML as @kirill-polishchuk correctly pointed out. If that is true code is even more simple:

        var values = from e in XElement.Load(filename).Descendants("a")
                         select e.Value;

Answer 5

As per OP comment, that input document is HTML, it'd be better to use HTML parser, e.g.: Html Agility Pack. You can use XPath //td/a to obtain desired result.

Answer 6

Using the HTML Agility Pack (project page, nuget), this does the trick:

HtmlDocument doc = new HtmlDocument();
doc.LoadHtml("your html here"); 
// or doc.Load(stream);

var nodes = doc.DocumentNode.DescendantNodes("a");
// or var nodes = doc.DocumentNode.SelectNodes("//td/a") ?? new HtmlNodeCollection();

foreach (var node in nodes)
{
    string city = node.InnerText;
}

// or var linkTexts = nodes.Select(node => node.InnerText);