title: How to convert a dataframe to a dictionary
body: <p>I have a dataframe with two columns and intend to convert it to a dictionary. The first column will be the key and the second will be the value.</p>
  <p>Dataframe:</p>
  <pre><code>    id    value
  0    0     10.2
  1    1      5.7
  2    2      7.4
  </code></pre>
  <p>How can I do this?</p>