title: Get unique list of chars used in a given column
body: <p>l have a <code>csv</code> file that l process with <code>pandas</code>. The column is called <code>raw_value</code> l want to retrieve the unique chars in this column.</p>
  
  <pre><code>x=df.manual_raw_value.unique()
  </code></pre>
  
  <p>allows to retrieve unique rows. However, l'm looking to retrieve the whole chars in this columns .
  which is  :
  alphabet= 6 , 3 5 1 8 V O T R E A 2 . é è /   : </p>
  
  <pre><code>   raw_value
      6,35
      11,68
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  </code></pre>
  
  <p><strong>EDIT_1</strong></p>
  
  <p>All the three solutions works perfectly.
  l chose the second one</p>
  
  <pre><code>set(df.raw_value.apply(list).sum())
  </code></pre>
  
  <p>Hwever it returns some encoded char. Is it related to encoding ?
  how to decode and display the real char . Here is what it prints </p>
  
  <pre><code>{' ',
   '!',
   '"',
   '%',
   '&amp;',
   "'",
   '(',
   ')',
   '*',
   '+',
   ',',
   '-',
   '.',
   '/',
   '0',
   '1',
   '2',
   '3',
   '4',
   '5',
   '6',
   '7',
   '8',
   '9',
   ':',
   '=',
   '&gt;',
   '?',
   '@',
   '_',
   'a',
   'b',
   'c',
   'd',
   'e',
   'f',
   'g',
   'h',
   'i',
   'j',
   'k',
   'l',
   'm',
   'n',
   'o',
   'p',
   'q',
   'r',
   's',
   't',
   'u',
   'v',
   'w',
   'x',
   'y',
   'z',
   '\x82',
   '\x87',
   '\x94',
   '\xa1',
   '\xa7',
   '\xaa',
   '\xab',
   '\xac',
   '\xae',
   '\xaf',
   '\xb0',
   '\xb4',
   '\xb9',
   '\xbb',
   '\xc2',
   '\xc3',
   '\xe2'}
  </code></pre>