null-sources on mallet composition file
<p>I want to use mallet for training topics. My data are in a single file, So I study mallet documentation to how construct this One Single file.</p>

<p>In <a href="http://mallet.cs.umass.edu/import.php" rel="nofollow noreferrer">Mallet website</a>, under the <strong>One file, one instance per line</strong> section, It was said:</p>

<blockquote>
  <p>[URL]  [language]  [text of the page...] </p>
  
  <p>In this case, the first token
  of each line (whitespace delimited, with optional comma) becomes the
  instance name, the second token becomes the label, and all additional
  text on the line is interpreted as a sequence of word tokens.</p>
</blockquote>

<p>So according to the above quote, I created my single file in this way:</p>

<pre><code>127  en  some text here...
982  en  some text here...
1003  en  some text here...
...
</code></pre>

<p>and then import this single file:</p>

<pre><code>bin\mallet import-file --input data.txt --output data.mallet --keep-sequence
</code></pre>

<p>after that, I train 3 topics:</p>

<pre><code>bin\mallet train-topics --input data.mallet --num-topics 3 --output-doc-topics data_composition.txt --word-topic-counts-file data_wcounts.txt
</code></pre>

<p>However, When I open the <code>data_composition.txt</code>, it has the following structure:</p>

<pre><code>#doc source topic proportion ...    
0 null-source 0 0.4057970941066742 1 0.3188405930995941 2 0.2753623127937317 
</code></pre>

<p>So now the question is: Why does mallet print <code>null-source</code> on this composition file? I want it prints the URL (i.e. IDs in my case) under the source heading.</p>

<p><strong>EDIT:</strong></p>

<p>I want something like this:</p>

<pre><code>#doc source topic proportion ...    
0     127   0 0.4057970941066742 1 0.3188405930995941 2 0.2753623127937317 
1     982    ... (topic probabilities) ...
2     1003   ... (topic probabilities) ...
</code></pre>

<p>thanks in advance! </p>