def merge_floats(values):
  """Return merged values as an average of floats (or None).

  Args:
    values: [str] of column values in sample equivalence class
  Returns:
    float: average of numeric values or None if no numeric values
  """
  v_sum = 0
  n_sum = 0
  for v in values:
    # Try to convert all column values to floats.
    try:
      x = float(v)
    # Ignore values that cannot be converted to a float.
    except ValueError:
      pass
    # Increment aggregate value
    else:
      v_sum += x
      n_sum += 1
      
  # Compute and return average value if it exists, else return None
  if n_sum <= 0:
    return None
  else:
    s = v_sum / n_sum
  return s