title: How could I select particular data and reform my data structure? csv python
body: <p>I have a matrix.csv file which looks like this, </p>
  
  <pre><code>  1,2,3,4 ............
  1,A,B,C,D
  2,E,F,G,H
  3,I,J,K,L
  4,M,N,P,Q
  .
  .
  .
  .
  </code></pre>
  
  <p>However, I only need a subset of the data (Because B is just E^-1, C is I^-1 and so on, which I do not need all of them.)</p>
  
  <pre><code>  1,2,3,4 ........
  1,A
  2,E,F
  3,I,J,K
  4,M,N,P,Q
  .
  .
  .
  .
  .
  </code></pre>
  
  <p>Then, I hope I can get a result.csv file looks like below,</p>
  
  <pre><code>1,1,A
  2,1,E
  2,2,F
  3,1,I
  3,2,J
  3,3,K
  4,1,M
  4,2,N
  4,3,P
  4,4,Q
  ....
  ....
  ....
  ....
  </code></pre>
  
  <p>I have tried to find a solution for the entire day, but I still cannot get it to work. Does anyone know how to solve with this problem by using python?</p>
  
  <p>Thanks,</p>