title: how to Find unique values in a column?Attribute Error: "DataFrame" object has no attribute
body: <p>I am making a generic tool which can take up any csv file.I have a csv file which looks something like this. The first row is the column name and the second row is the type of variable.</p>
  
  <pre><code>Time,M1,M2,M3,CityName
  temp,num,num,num,city
  20-May-13,19,20,0,aligarh
  20-May-13,25,42,7,agra
  20-May-13,23,35,4,aligarh
  20-May-13,21,32,3,allahabad
  20-May-13,17,27,1,aligarh
  20-May-13,16,40,5,aligarh
  </code></pre>
  
  <p>I want to find unique values in the column where the type of the variable is "city",i.e, the second row. I have been able to search the column name where the type is "city" and try to find the unique values but could not succeed further as it gives error.</p>
  
  <pre><code>filename = 'sam.csv'
  data_date = pd.read_csv(filename)
  column_name = data_date.ix[:, data_date.loc[0] == "city"]
  column_work = column_name.iloc[1:]
  name = column_work.dtypes.index
  column_unique = data_date.column_work.unique()
  print(column_unique)
  </code></pre>
  
  <p>I want the unique values in a list, such as,</p>
  
  <pre><code>[aligarh,agra,allahabad]
  </code></pre>