title: Count rows that have same value in all columns
body: <p>If I have a dataframe like this:</p>
  <pre><code>A  B  C  D  E  F      
  ------------------
  1  2  3  4  5  6
  1  1  1  1  1  1
  0  0  0  0  0  0
  1  1  1  1  1  1
  </code></pre>
  <p>How can I get the number of rows that have value <code>1</code> in every column?
  In this case, <strong>2</strong> rows have <code>1</code> in every field.</p>
  <p>I know one way, for example if we only take columns <code>A</code> and <code>B</code>:</p>
  <pre><code>count = df2.query(&quot;A == 1 &amp; B == 1&quot;).shape[0]
  </code></pre>
  <p>But I have to put the name of every column, is there a more fancy approach?</p>
  <p>Thanks in advance</p>