title: How to pivot categorical variable in pandas?
body: <p>How to pivot this data?</p>
  
  <pre><code>date - low - up
   d1  - a   - A
   d1  - b   - B
   d2  - c   - C
  </code></pre>
  
  <p>into this</p>
  
  <pre><code>low    a - b - c
  date   
   d1    A - B - NaN
   d2   NaN-NaN- C
  </code></pre>
  
  <p>I'm using pivot_table/pivot, but it always asking for numerical.
  How to pivot categorical variables? Thanks</p>