title: How to extract a vector from a large matrix by index in MATLAB?
body: <p>I am stucked with this issue in MATLAB for long now and I hope to find a help here!</p>
  
  <p>I have a very large matrix with 4 vectors in it (each vector is a column) and 72300 rows .. the first column/vector is the index of the data .. so it is something like this: (example is simplified)</p>
  
  <pre><code>Index, Info1  Info2  Info3
  1      2      1      1
  1      4      5      3
  1      2.5    1.3    8
  2      1      4      7
  2      4      6      9
  2      12     3      7
  3      2      6      6
  3      2      1      4
  3      1      4      7
  </code></pre>
  
  <p>Q1> How can I extract all Info2 with the index==3 from this matrix?</p>
  
  <p>Q2> Is there any method to rearrange the matrix to be like this?</p>
  
  <pre><code>Index,   Info1,   Info2 Info3   Index   Info1   Info 2  Info 3
   1                              2
  </code></pre>
  
  <p>and so on ..</p>
  
  <p>I hope to find some help from you guys and many many thanks in advance..</p>
  
  <p>kind regards,</p>