title: pandas dataFrame filter/derive scalar values from column
body: <p>My data is in a CSV that looks like this:</p>
  
  <pre><code>(m-M),err(m-M),D,Method,Refcode,Notes,SN Name,Redshift,H0,LMCModulus
  28.96,0.20,6.190,SNII optical,2017ApJ...841..127M,EPM,SN 2013ej,,,
  29.13,,6.700,SNII optical,2004A&amp;A...427..453V,EPM,SN 2002ap,,,
  29.29,,7.200,SNII optical,2006PASP..118..351V,,SN 2003gd,,,
  29.94,0.54,9.730,SNII optical,2010ApJ...715..833O,"SCM, I",SN 2003gd,,,
  29.98,0.28,9.910,SNII optical,2010ApJ...715..833O,"SCM, BVI",SN 2003gd,,,
  29.98,0.55,9.910,SNII optical,2010ApJ...715..833O,"SCM, V",SN 2003gd,,,
  29.99,0.42,9.950,SNII optical,2010ApJ...715..833O,"SCM, B",SN 2003gd,,,
  30.01,0.07,10.000,SNII optical,2014AJ....148..107R,"V, photospheric magnitude method",SN 2013ej,,,
  26.72,0.69,2.210,Tully-Fisher,1984A&amp;AS...56..381B,B,,,103.00,
  29.93,0.40,9.700,Tully-Fisher,1988NBGC.C....0000T,B,,,75.00,
  </code></pre>
  
  <p>My code is:</p>
  
  <pre><code>import pandas as pd,
  from pandas import DataFrame
  
  d = pd.read_csv('ngc0628_zid.csv')
  
  d  # Whole of the CSV prints OK
  
  d.loc[:, 'D':'Method']
  
  sub_d = d.loc[d['Method'] == 'SNII optical']   # Filter for 'SNII Optical' only - OK
  sub_d.loc[:, 'D':'Method']   # Just report columns 'D' and 'Method' - OK
  
  maxColumn = sub_d.max(axis=0)
  maxColumn     # Prints max of all values
  
  minColumn = sub_d.min(axis=0)
  minColumn     # Prints max of all values
  
  meanColumn = sub_d.mean(axis=0)
  meanColumn     # Prints mean of all values
  </code></pre>
  
  <p>Problem: I can't find a way to select the just 'D' column for processing mean, max, min without getting a syntax error. I can only get a table of values in each case, not the 3 scalars I need.</p>