我的数据结构如下（这些只是示例数据，因为原始数据是秘密的）
id | crime | location | crimedate
------------------------------
1 | Theft | public | 2019-01-04
1 | Theft | public | 2019-02-06
1 | Theft | public | 2019-02-20
1 | Theft | private | 2019-03-10
1 | Theft | private | 2019-03-21
1 | Theft | public | 2019-03-01
1 | Theft | private | 2019-03-14
1 | Theft | public | 2019-06-15
1 | Murder | private | 2019-01-04
1 | Murder | private | 2019-10-20
1 …