title: drop_duplicates not working in pandas?
body: <p>The purpose of my code is to import 2 Excel files, compare them, and print out the differences to a new Excel file.</p>
  
  <p>However, after concatenating all the data, and using the <code>drop_duplicates</code> function, the code is accepted by the console. But, when printed to the new excel file, duplicates still remain within the day.</p>
  
  <p>Am I missing something? Is something nullifying the <code>drop_duplicates</code> function?</p>
  
  <p>My code is as follows:</p>
  
  <pre><code>import datetime
  import xlrd
  import pandas as pd
  #identify excel file paths
  filepath = r"excel filepath"
  filepath2 = r"excel filepath2"
  #read relevant columns from the excel files
  df1 = pd.read_excel(filepath, sheetname="Sheet1", parse_cols= "B, D, G, O")
  df2 = pd.read_excel(filepath2, sheetname="Sheet1", parse_cols= "B, D, F, J")
  #merge the columns from both excel files into one column each respectively
  df4 = df1["Exchange Code"] + df1["Product Type"] + df1["Product Description"] + df1["Quantity"].apply(str)
  df5 = df2["Exchange"] + df2["Product Type"] + df2["Product Description"] + df2["Quantity"].apply(str)
  #concatenate both columns from each excel file, to make one big column containing all the data
  df = pd.concat([df4, df5])
  #remove all whitespace from each row of the column of data
  df=df.str.strip()
  df=["".join(x.split()) for x in df] 
  #convert the data to a dataframe from a series
  df = pd.DataFrame({'Value': df}) 
  #remove any duplicates
  df.drop_duplicates(subset=None, keep="first", inplace=False)
  #print to the console just as a visual aid
  print(df)
  #print the erroneous entries to an excel file
  df.to_excel("Comparison19.xls") 
  </code></pre>