title: Find Data between two consecutive nans
body: <p>So I have time series data that I do some calculations on it. I am stuck at trying to find a way to get the values of dates between nan points in the series.</p>
  <p>For example, the series looks like this:</p>
  <pre><code>            start_date  counts
  3  2021-10-14 20:12:13       0
  4  2021-10-14 20:21:10       1
  5  2021-10-14 20:22:15       2
  6  2021-10-14 20:23:14       3
  7  2021-10-14 20:23:51       4
  8  2021-10-14 20:39:11       0
  9  2021-10-14 20:41:21       1
  10 2021-10-14 20:41:45       2
  11 2021-10-14 20:42:10       3
  12 2021-10-14 20:46:10       4
  13 2021-10-14 20:52:53       5
  14 2021-10-14 20:53:10       6
  15 2021-10-14 20:56:10       7
  16 2021-10-14 20:57:46       8
  17 2021-10-14 20:59:25       9
  18 2021-10-14 21:00:12      10
  19 2021-10-14 21:02:24      11
  20 2021-10-14 21:06:13      12
  21 2021-10-14 21:09:12      13
  22 2021-10-14 21:11:35      14
  23 2021-10-14 21:16:30      15
  24 2021-10-14 21:19:12      16
  25 2021-10-14 21:32:14       0
  29 2021-10-14 23:52:07       0
  30 2021-10-14 23:57:41       1
  31 2021-10-15 00:06:14       2
  32 2021-10-15 00:23:25       0
  33 2021-10-15 00:32:09       1
  34 2021-10-15 00:54:11       0
  35 2021-10-15 01:03:13       1
  </code></pre>
  <p>I want to get the date of the first element ( always = 1) right next to date of the last element (16 in this case but could be any number more than 1)</p>
  <p>So the desired output should be :</p>
  <pre><code>2021-10-14 20:41:21 : 2021-10-14 21:19:12 
  .
  .
  etc.
  </code></pre>