title: How to lower all the elements in a pandas dataframe?
body: <p>Just a quick question guys, I have a pandas dataframe:</p>
  
  <pre><code>In [11]: df = pd.DataFrame([['A', 'B'], ['C', E], ['D', 'C']],columns=['X', 'Y', 'Z'])
  
  In [12]: df
  
  Out[12]: 
  
     X  Y  Z
  0  A  B  D
  1  C  E  C
  </code></pre>
  
  <p>How can I convert to lower all the elements of <code>df</code>:</p>
  
  <pre><code>Out[12]: 
  
     X  Y  Z
  0  a  b  d
  1  c  e  c
  </code></pre>
  
  <p>I look over the <a href="http://pandas.pydata.org/pandas-docs/stable/text.html" rel="noreferrer">documentation</a> and I tried the following:</p>
  
  <pre><code>df = [[col.lower() for col in [df["X"],df["Y"], df["Z"]]]]
  df
  </code></pre>
  
  <p>Nevertheless, it doesnt work. How to lower all the elements inside a pandas dataframe?.</p>