title: how to get values from an ArrayList<Hashtable<String, ArrayList<String>>>
body: <p>I have a function that is capable to read data from multiple files with the following structure:</p>
  
  <pre><code>id  date    temp    psal
  1   2016/02/01  37.6    35.9
  2   2016/02/02  30.3    35.7
  3   2016/02/03  28.2    36.8
  4   2016/02/04  27.7    37.7
  5   2016/02/05  28.7    37.9
  6   2016/02/06  28.7    37.9
  </code></pre>
  
  <p>The function is:</p>
  
  <pre><code>ArrayList&lt;Hashtable&lt;String, ArrayList&lt;String&gt;&gt;&gt; processedFilesArray = ReadFiles(files);
  </code></pre>
  
  <p>If I try to retrieve the data by using for example:</p>
  
  <pre><code>System.out.println(processedFilesArray.get(0));
  </code></pre>
  
  <p>Then I get the following response:</p>
  
  <pre><code>{Psals=[35.9, 35.7, 36.8, 37.7, 37.9, 37.9], Temps=[37.6, 30.3, 28.2, 27.7, 28.7, 28.7], ids=[1, 2, 3, 4, 5, 6], DateStrings=[2016/02/01, 2016/02/02, 2016/02/03, 2016/02/04, 2016/02/05, 2016/02/06]}
  </code></pre>
  
  <p>My question is:
  How can I obtain the different values of the keys (Temps, Psals, ids, etc) by sepparate to plot them using jfreechart?</p>
  
  <p>Thanks in advance</p>