code: @NonNull
      Collection<TObj> getColumnItems(int column) {
          Collection<TObj> result = new LinkedList<>();
          for (int count = mData.size(), i = 0; i < count; i++) {
              int key = mData.keyAt(i);
              TObj columnObj = mData.get(key).get(column);
              if (columnObj != null) {
                  result.add(columnObj);
              }
  
          }
          return result;
      }
docs: Get all column's items
  
  @param column column index
  @return Collection with column's Objects