       ...> "O N"  # real
       ...> ])
       ["GO", "PREDS"]
-
-  This ignores the special case of an empty string (""). Right now we leave in
-  the empty string as the first item to preserve the column index of the zone
-  groups.
-
-      iex> Mix.Tasks.Parcel.IngestLandUseTable.get_unmapped_zone_groups([
-      ...>  "WINGARDIUM",
-      ...>  "LEVIOSA",
-      ...>  ""   # ignored
-      ...> ])
-      ["WINGARDIUM", "LEVIOSA"]
   """
   def get_unmapped_zone_groups(zone_groups) do
-    actualy_zone_groups = zone_groups -- [""]
+    actualy_zone_groups = zone_groups
 
     actualy_zone_groups -- Map.keys(@zone_groups_to_zone_codes)
   end

  Rows at index 2 through 4 include identifiers of groups of zones:

    ,          ,....
    Agriculture, Residential,....
    AG   ,  RS280   , ...
    and   , thru   , ...
    AR2a  , RS3.75 , ...

  We translate these three lines into a single list of groups, e.g.
  ["AG and AR2a", "RS280 thru RS3.75"].  This can be used with
  @zone_groups_to_zone_codes to translate the table into information per
  zone code, even though we only receive information per zone group.

  Note that these come back preserving the order of the columns they are in.

  ## Examples
  A basic example:

      iex> Mix.Tasks.Parcel.IngestLandUseTable.get_zone_groups([
      ...>   ["Ignore", "these"],
      ...>   ["First", "two", "rows"],
      ...>   ["AG", "RS80"],
      ...>   ["and", "thru"],
      ...>   ["AR2a", "RS3.75-A"]
      ...> ])
      ["AG and AR2a", "RS80 thru RS3.75-A"]


      ...>   "c"
      ...> ])
      %{"a" => [2, 1, 0], "b" => [3], "c" => [4]}
  """
  def sparsify_unique(list, empty \\ "") do
    {sparsified, _} = Stream.with_index(list)
