title: Fill in pd data frame into existing excel sheet (using openpyxl v2.3.2)
body: <p>I want to fill in some pandas data frames into an <strong>existing</strong> excel file. I followed the instructions in:
  <a href="https://stackoverflow.com/questions/20219254/how-to-write-to-an-existing-excel-file-without-overwriting-data-using-pandas">How to write to an existing excel file without overwriting data (using pandas)?</a>
  using:</p>
  
  <pre><code>  from openpyxl import load_workbook
    import pandas as pd
    import numpy as np
  
    book=load_workbook("excel_proc.xlsx")
    writer=pd.ExcelWriter("excel_proc.xlsx", engine="openpyxl")
    writer.book = book
    writer.sheets = dict((ws.title, ws) for ws in book.worksheets)
    data_df.to_excel(writer, sheet_name="example", startrow=100, startcol=5, index=False)
    writer.save()
  </code></pre>
  
  <p>However, the existing sheets will be deleted, the "example" sheet is generated and only the df is integrated at the defined location. What did I do wrong? I want the "data_df" written into the existing excel file in the existing "example" sheet, keeping the other sheets and data.</p>
  
  <p>Thanks</p>
  
  <p>Example df:</p>
  
  <pre><code>data_df=pd.DataFrame(np.arange(12).reshape((2, 6)), index=["Time","Value"])
  </code></pre>