title: find first instance of a row in pandas dataframe matching a criterion
body: <p>I have a dataframe giving event time (in days) and a value associated with each event.  </p>
  
  <p>sorry for placing this in as code snippet, not sure of any other way to show format as a table in this question.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>+-----------+----------+
  | EventTime |  Value   |
  +-----------+----------+
  | 389.9067  | 0.076014 |
  | 670.9632  | 0.190521 |
  | 1012.2839 | 0.266599 |
  | 1025.2452 | 0.355095 |
  | 1347.1064 | 0.45189  |
  | 3554.909  | 0.64213  |
  | 3932.491  | 0.688693 |
  | 4450.6369 | 0.730536 |
  | 4819.5832 | 0.746905 |
  | 6252.0017 | 0.880531 |
  | 6951.3345 | 0.898307 |
  | 7607.0877 | 0.945048 |
  | 9044.0014 | 1.002455 |
  | 9433.6679 | 1.083201 |
  +-----------+----------+</code></pre>
  </div>
  </div>
  </p>
  
  <p>I am interested in obtaining the event time associated with the first value >= a given input, e.g. if input =0.40, I want to report 1347.1064</p>
  
  <p>Ideally, I would like a general solution where I supply a list of value thresholds and the dataframe, e.g. (.4, .7, .9) and obtain back a list (or any other data structure) with the corresponding event times.</p>
  
  <p>Looked around, did not see anything obvious in terms of a solution, but probably just missing something or my ignorance of pandas, trying to learn.</p>
  
  <p>Thanks in advance</p>