title: "A value is trying to be set on a copy of a slice from a DataFrame" warning avoidance
body: <p>I try to run this code in a Jupyter environment and I get "A value is trying to be set on a copy of a slice from a DataFrame" in spite of the the fact that I am using  df.loc .</p>
  
  <p>How do I avoid this error message for the following code? All I am trying to do is round the values in the 'Score' column.</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  
  data = [['Orange',11.111],['Orange',12.1111111],['Orange',13.111111],
          ['Orange',14.11111],['Orange',15.111111],['Orange',16.111111],
          ['Orange',17.11111],['Orange',18.11111], 
          ['StrawBerry',22.11111],['StrawBerry',23.11111],
          ['StrawBerry',24.11111], 
          ['StrawBerry',25.11111],['StrawBerry',26.11111], 
          ['StrawBerry',27.111111]]
  
  df = pd.DataFrame(data,columns=['Fruit', 'Score'])
  df
  
  df['Score'] = df.loc[:,'Score'].apply(lambda x: np.round(x,decimals=4))
  
  print (df['Score'])
  print (df)
  </code></pre>