title: Count number of 0's in a particular column
body: <p>I have a csv which has the following columns </p>
  
  <pre><code>Date    isAccepted
  </code></pre>
  
  <p>There are many repeated dates and isAccepted is a boolean value column with 0 and 1. I want to calculate count of 0's for a particular date. </p>
  
  <p>I am trying this : </p>
  
  <pre><code>df['Count'] = df.groupby('Date').apply(lambda isAccepted: (isAccepted == 0).sum())
  </code></pre>
  
  <p>But the column returned is NaN. Can anyone tell whats wrong with the code. </p>
  
  <p>Thanks</p>