code: public AttributeVector column(String col) {
          int i = -1;
          for (int j = 0; j < attributes.length; j++) {
              if (attributes[j].getName().equals(col)) {
                  i = j;
                  break;
              }
          }
  
          if (i == -1) {
              throw new IllegalArgumentException("Invalid column name: " + col);
          }
  
          return column(i);
      }
docs: Returns a column.