title: Finding the index of the first element (e.g "True") from a series/column
body: <p>How do I find the index of an element (e.g "True") in a series or a column?</p>
  
  <p>For example I have a column, where I want to identify the first instance where an event occur. So I write it as </p>
  
  <pre><code>Variable = df["Force"] &lt; event
  </code></pre>
  
  <p>This then creates a boolen series of Data where it is False, until the first instance it becomes True. How then do I find the index of data point? </p>
  
  <p>Is there are better way?</p>