title: Group a List<object[]>
body: <p>I have a question that's similar to <a href="https://stackoverflow.com/questions/13962393/group-and-sum-a-listobject">yesterday's question</a>.<br />
  I've got this List&lt;object[]&gt;</p>
  
  <pre><code>List&lt;object[]&gt; olst = new List&lt;object[]&gt;();
  
  olst.Add(new object[] { "AA1", "X", 1, 3.50 });
  olst.Add(new object[] { "AA2", "Y", 2, 5.20 });
  olst.Add(new object[] { "AA2", "Y", 1, 3.50 });
  olst.Add(new object[] { "AA1", "X", 1, 3.20 });
  olst.Add(new object[] { "AA1", "Y", 2, 5.30 });
  </code></pre>
  
  <p>I need to produce List&lt;object[]&gt; to hold this:</p>
  
  <pre><code>"AA1", "X", 2, 6.70
  "AA2", "Y", 3, 8.70
  "AA1", "Y", 2, 5.30
  </code></pre>
  
  <p>In other words, I need to group olst by the <strong>1st</strong> and <strong>2nd</strong> elements of each object[] and sum <strong>3rd</strong> and <strong>4th</strong>.<br />
  I could use a for loop, but I was hoping someone could help me using lambda expressions and/or linq to accomplish this.</p>