title: dataframe to dict such that one column is the key and the other is the value
body: <p>I have the dataframe</p>
  
  <pre><code>    ID   A   B   C
  0   p    1   3   2
  1   q    4   3   2
  2   r    4   0   9  
  </code></pre>
  
  <p>And I want to create a dict where ID is the keys and B is the values so it will be:</p>
  
  <p><code>d["q"] = 3 , d["r"] = 0</code></p>
  
  <p>What is the best way to do so?</p>
  
  <p>It is different than the supposed duplicate becasue I want single value per key and not a list</p>