title: Python Pandas - change column within group if condition is met
body: <p>I have a dataframe <code>df</code> with column 'Batch' and 'Status'. 'Status' has the possible values 'keep' or 'remove'. I want to make a new column 'Status updated', which is 'keep' only if all elements for the same Batch number in 'Status' are 'keep' and 'remove' otherwise.</p>
  <pre><code>    Batch  Status
  0       1    keep
  1       1    keep
  2       1  remove
  3       2    keep
  4       2    keep
  5       2    keep
  6       3  remove
  7       3  remove
  8       3    keep
  9       4  remove
  10      4  remove
  11      4  remove
  </code></pre>
  <p>Desired output looks like:</p>
  <pre><code>Batch  Status Status updated
  0       1    keep         remove
  1       1    keep         remove
  2       1  remove         remove
  3       2    keep           keep
  4       2    keep           keep
  5       2    keep           keep
  6       3  remove         remove
  7       3  remove         remove
  8       3    keep         remove
  9       4  remove         remove
  10      4  remove         remove
  11      4  remove         remove
  </code></pre>