title: determine length (or number of digits) of every row in column
body: <p>I have a dataframe with columns that are <code>floats</code>. Some rows have <code>NaN</code> values.</p>
  
  <p>I want to find rows where the length (or number of digits) of the number is <code>!=6</code>. </p>
  
  <p>I tried the following:</p>
  
  <pre><code>len(str(df['a'])) != 6
  </code></pre>
  
  <p>But this seems to only return only one Boolean value and not a Boolean for every row in the dataframe. </p>
  
  <p>What is the correct way to do this? </p>
  
  <p><strong>UPDATE</strong>:</p>
  
  <p>Someone made a post with an answer similar to:</p>
  
  <pre><code>df.query('a &lt;= 10**5')
  </code></pre>
  
  <p>That seemed to work nicely. Now, I want to add an additional condition where column b is not null. How do I do that in the query() function. </p>