def read_data_as_dataframe(self,<EOL>travel_impedance_measure,<EOL>from_stop_I=None,<EOL>to_stop_I=None,<EOL>statistic=None):
to_select = []<EOL>where_clauses = []<EOL>to_select.append("<STR_LIT>")<EOL>to_select.append("<STR_LIT>")<EOL>if from_stop_I is not None:<EOL><INDENT>where_clauses.append("<STR_LIT>" + str(int(from_stop_I)))<EOL><DEDENT>if to_stop_I is not None:<EOL><INDENT>where_clauses.append("<STR_LIT>" + str(int(to_stop_I)))<EOL><DEDENT>where_clause = "<STR_LIT>"<EOL>if len(where_clauses) > <NUM_LIT:0>:<EOL><INDENT>where_clause = "<STR_LIT>" + "<STR_LIT>".join(where_clauses)<EOL><DEDENT>if not statistic:<EOL><INDENT>to_select.extend(["<STR_LIT>", "<STR_LIT>", "<STR_LIT>", "<STR_LIT>"])<EOL><DEDENT>else:<EOL><INDENT>to_select.append(statistic)<EOL><DEDENT>to_select_clause = "<STR_LIT:U+002C>".join(to_select)<EOL>if not to_select_clause:<EOL><INDENT>to_select_clause = "<STR_LIT:*>"<EOL><DEDENT>sql = "<STR_LIT>" + to_select_clause + "<STR_LIT>" + travel_impedance_measure + where_clause + "<STR_LIT:;>"<EOL>df = pd.read_sql(sql, self.conn)<EOL>return df<EOL>
Recover pre-computed travel_impedance between od-pairs from the database.

Returns
-------
values: number | Pandas DataFrame