function clean_row(row, column_medians):

   for column, value in row:
      if value is missing:
        row[column] = column_medians[column] # impute
   return row

 function one_hot_encode(category, all_categories):

   return [1 if category == c else 0 for c in all_categories]

 one_hot_encode("red", ["red", "green", "blue"]) # [1, 0, 0]
