title: sorting row by logic conditions pandas
body: <p>I am trying to sort rows within column sample.single by excluding ('./.'). The all data types are objects. I have attempted the options below. I suspect the special character is compromising the second attempt. Dataframe is comprised of 195 columns.</p>
  
  <p>My gtdata columns: </p>
  
  <p>Index(['sample.single', 'sample2.single', 'sample3.single'] dtype='object')</p>
  
  <p>Please advise, thank you!</p>
  
  <pre><code>gtdata = gtdata[('sample.single')!= ('./.') ]
  </code></pre>
  
  <p>I receive a key error: KeyError: True</p>
  
  <p>When I try:</p>
  
  <pre><code>gtdata = gtdata[gtdata.sample.single != ('./.') ]
  </code></pre>
  
  <p>I receive an attribute error:</p>
  
  <p>AttributeError: 'DataFrame' object has no attribute 'single'</p>