code: public int columnIndex(final String columnName) {
      Integer index = _columnNamesToIndices.get(columnName);
      if (index == null) {
        throw new IllegalArgumentException("Could not find index for column " + columnName);
      }
      return index;
    }
docs: Get the column index of the named column (zero-based). Throws IllegalArgumentException if column of provided name is not found.
  Repeated column names can be indexed as column, column.1, column.2, etc.
  
  @param columnName the name of the column
  @return the column index