我需要帮助从文档中获取具有字段(级别)最大值的数组元素。然后统计数组元素字段“bssid”分组的总出现次数。考虑以下数据/*1*/{"_id":"18:59:36:0c:94:a3","timestamp":"1460012567","apdata":[{"bssid":"f4:b7:e2:56:e4:20","ssid":"TestNetwork2","level":-55},{"bssid":"b8:a3:86:67:03:56","ssid":"TestNetwork1","level":-76}]}/*2*/{"_id":"d0:b3:3f:b9:42:38","timesta