Need help for solution on grouping a group

[Juan Marvin]

Hi All,

Here is my data about mac addresses. It is recorded per minute. For each minute, I have many unique Mac addresses. Each mac addresses have different "created_time" and different "log in" time length.

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,2016-12-07 00:01:00.000

...

I would like to create 2 bar charts using dc.js and crossfilter. Please refer to the image for the charts.

The first bar chart is easy enough to create. It is brush-able. I created the "created_time" dimension, and created a group and reduceCount by "mac_add", such as below:

var moveTime = ndx.dimension(function (d) {

                    return d.dd; //# this is the created_time

                });

var timeGroup = moveTime.group().reduceCount(function (d) {

                    return d.mac_add;

                });

var visitorChart = dc.barChart('#visitor-no-bar');

visitorChart.width(990) 

                .height(350)

                .margins({ top: 0, right: 50, bottom: 20, left: 40 })

                .dimension(moveTime)

                .group(timeGroup)

                .centerBar(true)

                .gap(1)

                .elasticY(true)

                .x(d3.time.scale().domain([new Date(2016, 11, 7), new Date(2016, 11, 13)]))

                .round(d3.time.minute.round)

                .xUnits(d3.time.minute);

visitorChart.render();

The problem happens on the second bar chart. The idea is that, one row of the data equals 1 minute, so I can aggregate and sum all minutes of each mac address to get the time length of each mac addresses, by creating another dimension by "mac_add" and do reduceCount on "mac_add" to get the time length. Then the goal is to group the time length by 30 minutes. So we can get how many mac address that have time length of 30 min and less, how many mac_add that have time length between 30 min and 1 hour, how many mac_add that have time length between 1 hour and 1.5 hour, etc...

Please correct me if I am wrong. Logically, I was thinking the dimension of the second bar chart should be the group of time length (such as <30, <1hr, < 1.5hr, etc). But the time length group themselves are not fix. It depends on the brush selection of the first chart. Maybe it only contains 30 min, maybe it only contains 1.5 hours, maybe it contains 1.5 hours and 2 hours, etc...

So I am really confused what parameters to put into the second bar chart. And method to get the required parameters (how to group a grouped data). Please help me to explain the solution.

Regards,

Marvin