[R] xml newbie

[Alexander Coppock]

Dear r-helpers,

I am trying to extract quantities of interest from my iTunes library xml file. 
 For example, i'd like to be able to run a simple regression of playcount on 
track number, under the theory that tracks near the beginning of albums get 
played more (either because they are "better" or because people listen to the 
beginnings of albums)

I have an xml file that is of the following form:

<key>13162</key>
<dict>
<key>Track ID</key><integer>13162</integer>
<key>Name</key><string>I'm A Wheel</string>
<key>Artist</key><string>Wilco</string>
<key>Composer</key><string>Jeff Tweedy</string>
<key>Album</key><string>A Ghost is Born</string>
<key>Genre</key><string>Rock</string>
<key>Kind</key><string>Matched AAC audio file</string>
<key>Size</key><integer>6248701</integer>
<key>Total Time</key><integer>154648</integer>
<key>Disc Number</key><integer>1</integer>
<key>Disc Count</key><integer>1</integer>
<key>Track Number</key><integer>9</integer>
<key>Track Count</key><integer>12</integer>
<key>Year</key><integer>2004</integer>
<key>Date Modified</key><date>2012-07-26T22:29:15Z</date>
<key>Date Added</key><date>2010-01-27T00:02:21Z</date>
<key>Bit Rate</key><integer>256</integer>
<key>Sample Rate</key><integer>44100</integer>
<key>Play Count</key><integer>3</integer>
<key>Play Date</key><integer>3434905791</integer>
<key>Play Date UTC</key><date>2012-11-05T00:29:51Z</date>
<key>Artwork Count</key><integer>1</integer>
<key>Sort Album</key><string>Ghost is Born</string>
<key>Persistent ID</key><string>A8B0E5CF2E86A4C6</string>
<key>Track Type</key><string>File</string>
<key>Location</key><string>file://localhost/Users/Alex/Music/iTunes/iTunes%20Media/Music/Wilco/A%20Ghost%20is%20Born/09%20I'm%20A%20Wheel.m4a</string>
<key>File Folder Count</key><integer>5</integer>
<key>Library Folder Count</key><integer>1</integer>
</dict> 


>From each entry, i'd like to extract: Track ID, Track Number and Play Count.  
>In this case, it would be 

13162, 9, 3

my guess is that this can be done using library(XML).

If anyone has any guidance, it would be appreciated.  Please note: 

a) I do not understand XML data structures, so please explain what you mean by 
"children" etc…
b) Not every entry in my database has a track number and a play count -- i'd 
like to have NAs associated with the appropriate Track ID, which all entries 
have.
c) it'd also be OK if this XML database just got turned into a normal r data 
frame.

Thanks!
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