 class="n">df</span><span class="p">[</span><span class="s2">&quot;nobs&quot;</span><span class="p">]</span>
              <span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="n">np</span><span class="o">.</span><span class="n">nan</span><span class="p">,</span> <span class="n">titanic</span><span class="o">.</span><span class="n">shape</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
              <span class="o">.</span><span class="n">