exercise3():
  Get a datafile in csv format from the class website.
  Read the data from the datafile.
  Print the first five lines.
  Convert the numeric columns 3, 4, 5, to a numpy array.
  Compute some statistical measurements.
  When finished, delete the datafile.
  Downloading dataset file:

  First five lines of df:

Traceback (most recent call last):
  File "exercise3.py", line 136, in <module>
    exercise3 ( )
  File "exercise3.py", line 64, in exercise3
    print ( '(', i, ')', df[i,:] )
  File "/home/burkardt/.local/lib/python3.6/site-packages/pandas/core/frame.py", line 2800, in __getitem__
    indexer = self.columns.get_loc(key)
  File "/home/burkardt/.local/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2646, in get_loc
    return self._engine.get_loc(key)
  File "pandas/_libs/index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 116, in pandas._libs.index.IndexEngine.get_loc
TypeError: '(0, slice(None, None, None))' is an invalid key