title: Ignoring NaN in a dataframe
body: <p>I want to find the unique elements in a column of a dataframe which have missing values. i tried this: <code>df[Column_name].unique()</code> but it returns nan as one of the elements. what can i do to just ignore the missing values.
  dataframe look like this.<a href="https://i.stack.imgur.com/emLdk.jpg" rel="noreferrer">click here</a></p>