title: concatColumn pops out UnsupportedOperationException
body: <p>I am doing a simple Data Frame that can read and write CSV while being able to edit the data. I have encountered a problem when I am trying to concatenate a new column to my data frame.</p>
  <p>This is the sample input of the file:</p>
  <pre><code>Name,Age,Salary
  Lim,20,2000
  Tan,20,3000
  Mah,19,2500
  Roger,10,4000
  </code></pre>
  <p>And this is my code to concatenate the columns :</p>
  <pre><code>String filePath = &quot;\...\Book1.csv&quot;;
  
  String line;
  List&lt;List&lt;String&gt;&gt; data = new ArrayList();
  
  try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
      while ((line = br.readLine()) != null) {
          List&lt;String&gt; column = Arrays.asList(line.split(&quot;,&quot;));
          data.add(column);
      }
  
  } catch (Exception e) {
      System.out.println(e);
  }
  
  System.out.println(data.toString());
  
  String [] newColumn = {&quot;Colour&quot;, &quot;Green&quot;, &quot;Blue&quot;, &quot;Black&quot;,&quot;Yellow&quot;};
  for(int i = 0 ; i&lt;data.size(); i++){
      List&lt;String&gt; temp = data.get(i);
      temp.add(newColumn[i]);
  }
  
  System.out.println(data.toString());
  </code></pre>
  <p>The output will be like this :</p>
  <pre><code>[[Name, Age, Salary], [Lim, 20, 2000], [Tan, 20, 3000], [Mah, 19, 2500], [Roger, 10, 4000]]
  Exception in thread &quot;main&quot; java.lang.UnsupportedOperationException
      at java.base/java.util.AbstractList.add(AbstractList.java:153)
      at java.base/java.util.AbstractList.add(AbstractList.java:111)
      at Testing.main(Testing.java:31)
  
  System.out.println(data.toString());
  </code></pre>
  <p>How am I going to change the code to be able to read the <code>newColumn</code> and store it into <code>data</code>?</p>