protected String extractGroupFromId(String columnName) {
        if (columnName == null || !columnName.contains(idSeparator)) return columnName;
        String[] tokens = columnName.split(idSeparator);
        if (tokens.length == 2) {
            return tokens[0];
        } else {
            throw new IllegalArgumentException(String.format("Cannot extract row key from column name string: %s", columnName));
        }
    }
protected String extractGroupFromId(String columnName) {
        if (columnName == null || !columnName.contains(idSeparator)) return columnName;
        String[] tokens = columnName.split(idSeparator);
        if (tokens.length == 2) {
            return tokens[0];
        } else {
            throw new IllegalArgumentException(String.format("Cannot extract row key from column name string: %s", columnName));
        }
    }
protected String extractGroupFromId ( String columnName ) { if ( columnName == null || ! columnName . contains ( idSeparator ) ) return columnName ; String [ ] tokens = columnName . split ( idSeparator ) ; if ( tokens . length == 2 ) { return tokens [ 0 ] ; } else { throw new IllegalArgumentException ( String . format ( "Cannot extract row key from column name string: %s" , columnName ) ) ; } }
@warn method description missing
@warn parameter columnName description missing
@warn exception IllegalArgumentException description missing

@param columnName
@return
@throws IllegalArgumentException
@warn method description missing @warn parameter columnName description missing @warn exception IllegalArgumentException description missing