Parsing Last.fm Web Services' artist.getSimilar with C# and LINQ to XML

The following covers how to parse the XML response of artist.getSimilar, from Last.fm's Web Services.

Setup and assumptions

The first step is sign up for a free API account at Last.fm.

You'll also need to target .NET Framework 3.5 when you setup your project, so as to access LINQ functionality.

When writing the steps listed below, I was working on a Windows Forms Application, but the steps should be the same, or very similar, for other project types.

Creating the base class

The first thing I've done is created a new class file in my project called Lastfm.cs, resulting in the following.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace JamesRSkemp.WebServices {
class Lastfm {
private const string LastFmApiKey = “EnterYourApiKeyHere”;


}



}

We'll add a new method to the Lastfm class to return the base Url we'll need to make Web service requests.

		/// <summary>
		/// Get the base Url that we'll use to make Web service requests.
		/// </summary>
		/// <returns>The base Url to use to make Web service requests.</returns>
		static private string GetBaseRequestUrl() {
			string baseUrl = "http://ws.audioscrobbler.com/2.0/?api_key=" + LastFmApiKey;
			return baseUrl;
		}

Next we'll create a method to make a request to a Web service and return the full response.

		/// <summary>
		/// Gets the data from an HTTP request.
		/// </summary>
		/// <param name="requestUrl">The full Url of the request to make.</param>
		/// <returns>Returns a string with the text returned from the request.</returns>
		private string GetServiceResponse(string requestUrl) {
			string httpResponse = "";

		HttpWebRequest request = (HttpWebRequest)WebRequest.Create(requestUrl);
		request.Timeout = 15000;
		HttpWebResponse response = null;
		StreamReader reader = null;

		try {
			response = (HttpWebResponse)request.GetResponse();
			reader = new StreamReader(response.GetResponseStream());

			httpResponse = reader.ReadToEnd();
		} finally {
			if (reader != null) {
				reader.Close();
			}
			if (response != null) {
				response.Close();
			}
		}

		return httpResponse;
	}</code></pre>



The following references must also be added.


using System.Net;
using System.IO;


When we use this class, we want to have our data returned in an easy to use format. For ease, we'll have it return a DataTable. We'll have to add the appropriate reference first.


using System.Data;


We can then began our method as follows.


		public DataTable GetSimilarArtists(string artistName) {
			if (String.IsNullOrEmpty(artistName)) {
				throw new Exception("Artist name must be populated.");
			} else {
				string requestUrl = GetBaseRequestUrl();
				requestUrl += "&method=artist.getSimilar&artist=" + System.Web.HttpUtility.UrlEncode(artistName.Trim());

			string serviceResponse = GetServiceResponse(requestUrl);

			DataTable similarArtists = new DataTable();
			
			// TODO

			return similarArtists;
		}
	}</code></pre>



If we were to make a request now, we'd see that the data returned is formatted similar to the following, for a request for Bruce Springsteen. (For ease and sanity, data truncated.)


<?xml version="1.0" encoding="utf-8"?>
<lfm status="ok">
<similarartists artist="Bruce Springsteen">
<artist>
    <name>Bruce Springsteen & The E Street Band</name>
    <mbid>5a1283bf-81d5-4700-8919-683eeaaf2beb</mbid>
    <match>100</match>
    <url>www.last.fm/music/Bruce%2BSpringsteen%2B%2526%2BThe%2BE%2BStreet%2BBand</url>
    <image size="small">http://userserve-ak.last.fm/serve/34/8415485.jpg</image>
    <image size="medium">http://userserve-ak.last.fm/serve/64/8415485.jpg</image>
    <image size="large">http://userserve-ak.last.fm/serve/126/8415485.jpg</image>
    <image size="extralarge">http://userserve-ak.last.fm/serve/252/8415485.jpg</image>
    <image size="mega">http://userserve-ak.last.fm/serve/500/8415485/Bruce+Springsteen++The+E+Street+Band+estreet.jpg</image>
    <streamable>1</streamable>
</artist>
[...]
</similarartists></lfm>


We'd first need to add a reference so that we can parse through the returned response.


using System.Xml.Linq;


We can now create our LINQ to XML query to access the similar artist's name and match percentage.


				var xmlResponse = XElement.Parse(serviceResponse);

			// Parse through the returned Xml for the name and match value for each similar artist.
			var artists = from artistsSimilar in xmlResponse.Descendants("artist")
						  select new {
							  name = artistsSimilar.Element("name").Value,
							  match = artistsSimilar.Element("match").Value
						  };</code></pre>



Next we can create the DataTable that we'll use to store the name and math values.


				DataTable similarArtists = new DataTable();
				similarArtists.Columns.Add("Artist");
				similarArtists.Columns.Add("Match", System.Type.GetType("System.Double"));


Finally we can loop through each result returned from our LINQ to XML query, adding a new row to the table, for each.


				if (artists.Count() > 0) {
					DataRow artistsRow;
					foreach (var artist in artists) {
						artistsRow = similarArtists.NewRow();
						artistsRow["Artist"] = artist.name;
						artistsRow["Match"] = artist.match;
						similarArtists.Rows.Add(artistsRow);
					}
				}


Finally we return the populated DataTable.


				return similarArtists;


Assuming a Windows Form Application with a text box (textBox1), a DataGridView (dataGridView1), and a button (button1), we could do the following (assuming the appropriate references have been added).


		private void button1_Click(object sender, EventArgs e) {
			if (!String.IsNullOrEmpty(textBox1.Text)) {
				Lastfm lastFmRequest = new Lastfm();

			DataTable results = lastFmRequest.GetSimilarArtists(textBox1.Text);

			dataGridView1.DataSource = results;
		} else {
			MessageBox.Show("You must enter an artist to continue.");
			textBox1.Focus();
		}
	}</code></pre>



Taken together, that results in the following. (Download JamesRSkemp.WebServices.Lastfm.cs.)


/*
Created by James Skemp - http://jamesrskemp.com/
Version 1.0
More information at http://strivinglife.com/words/post/Parsing-Lastfm-Web-Services-artistgetSimilar-with-C-and-LINQ-to-XML.aspx
Shared under a Creative Commons Attribution 3.0 United States License - http://creativecommons.org/licenses/by/3.0/us/
*/
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.IO;
using System.Data;
using System.Xml.Linq;

namespace JamesRSkemp.WebServices {
class Lastfm {
/// <summary>
/// Key used to access Last.fm Web services.
/// </summary>
private const string LastFmApiKey = “EnterYourApiKeyHere”;


	/// &lt;summary&gt;
	/// Return artists similar to the one passed, with a match percentage.
	/// &lt;/summary&gt;
	/// &lt;param name="artistName"&gt;The name of the artist to use for the request.&lt;/param&gt;
	/// &lt;returns&gt;DataTable with artist names and match percentage, as a Double.&lt;/returns&gt;
	public DataTable GetSimilarArtists(string artistName) {
		if (String.IsNullOrEmpty(artistName)) {
			throw new Exception("Artist name must be populated.");
		} else {
			string requestUrl = GetBaseRequestUrl();
			requestUrl += "&amp;method=artist.getSimilar&amp;artist=" + System.Web.HttpUtility.UrlEncode(artistName.Trim());

			string serviceResponse = GetServiceResponse(requestUrl);

			var xmlResponse = XElement.Parse(serviceResponse);

			// Parse through the returned Xml for the name and match value for each similar artist.
			var artists = from artistsSimilar in xmlResponse.Descendants("artist")
						  select new {
							  name = artistsSimilar.Element("name").Value,
							  match = artistsSimilar.Element("match").Value
						  };

			DataTable similarArtists = new DataTable();
			similarArtists.Columns.Add("Artist");
			similarArtists.Columns.Add("Match", System.Type.GetType("System.Double"));

			if (artists.Count() &gt; 0) {
				DataRow artistsRow;
				foreach (var artist in artists) {
					artistsRow = similarArtists.NewRow();
					artistsRow["Artist"] = artist.name;
					artistsRow["Match"] = artist.match;
					similarArtists.Rows.Add(artistsRow);
				}
			}

			return similarArtists;
		}
	}

	/// &lt;summary&gt;
	/// Get the base Url that we'll use to make Web service requests.
	/// &lt;/summary&gt;
	/// &lt;returns&gt;The base Url to use to make Web service requests.&lt;/returns&gt;
	private string GetBaseRequestUrl() {
		string baseUrl = "http://ws.audioscrobbler.com/2.0/?api_key=" + LastFmApiKey;
		return baseUrl;
	}

	/// &lt;summary&gt;
	/// Gets the data from an HTTP request.
	/// &lt;/summary&gt;
	/// &lt;param name="requestUrl"&gt;The full Url of the request to make.&lt;/param&gt;
	/// &lt;returns&gt;Returns a string with the text returned from the request.&lt;/returns&gt;
	private string GetServiceResponse(string requestUrl) {
		string httpResponse = "";

		HttpWebRequest request = (HttpWebRequest)WebRequest.Create(requestUrl);
		request.Timeout = 15000;
		HttpWebResponse response = null;
		StreamReader reader = null;

		try {
			response = (HttpWebResponse)request.GetResponse();
			reader = new StreamReader(response.GetResponseStream());

			httpResponse = reader.ReadToEnd();
		} finally {
			if (reader != null) {
				reader.Close();
			}
			if (response != null) {
				response.Close();
			}
		}

		return httpResponse;
	}
}



}


Advanced error handling is missing, but this should give you a basic idea of how you can go about easily accessing Last.fm's Web Services, and parsing returned data.


Final thoughts


Questions? Comments? Concerns? Please add a comment below.


Updated 9/12/2009, 15:55: I was doing it in my implementation, but added simple check for a populated textBox1 to the above code.
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