crossfilter “double grouping” where key is the value of another reduction
问题 Here is my data about mac address. It is recorded per minute. For each minute, I have many unique Mac addresses. mac_add,created_time 18:59:36:12:23:33,2016-12-07 00:00:00.000 1c:e1:92:34:d7:46,2016-12-07 00:00:00.000 2c:f0:ee:86:bd:51,2016-12-07 00:00:00.000 5c:cf:7f:d3:2e:ce,2016-12-07 00:00:00.000 ... 18:59:36:12:23:33,2016-12-07 00:01:00.000 1c:cd:e5:1e:99:78,2016-12-07 00:01:00.000 1c:e1:92:34:d7:46,2016-12-07 00:01:00.000 5c:cf:7f:22:01:df,2016-12-07 00:01:00.000 5c:cf:7f:d3:2e:ce,2016