title: Standard deviation of a list
body: <p>I want to find mean and standard deviation of 1st, 2nd,... digits of several (Z) lists. For example, I have</p>
  
  <pre><code>A_rank=[0.8,0.4,1.2,3.7,2.6,5.8]
  B_rank=[0.1,2.8,3.7,2.6,5,3.4]
  C_Rank=[1.2,3.4,0.5,0.1,2.5,6.1]
  # etc (up to Z_rank )...
  </code></pre>
  
  <p>Now I want to take the mean and std of <code>*_Rank[0]</code>, the mean and std of <code>*_Rank[1]</code>, etc.<br>
  (ie: mean and std of the 1st digit from all the (A..Z)_rank lists;<br>
  the mean and std of the 2nd digit from all the (A..Z)_rank lists;<br>
  the mean and std of the 3rd digit...; etc). </p>