Number of Unique Values Using CrossFilter

Question

CrossFilter/JS newbie here.

This question pretty much describes exactly what I'm trying to do but there doesn't seem to be a solution using CrossFilter:

How to return the number of unique values by category using crossfilter?

I have data with

var va = [{ date: "2014-10-01", id: "1"}, { date: "2014-10-02", id: "1"}, { date: "2014-10-03", id: "1"}, { date: "2014-10-04", id: "1"}, { date: "2014-10-05", id: "1"}, { date: "2014-10-01", id: "2"}, { date: "2014-10-02", id: "2"}, { date: "2014-10-03", id: "2"}, { date: "2014-10-04", id: "1"}, { date: "2014-10-01", id: "3"}, { date: "2014-10-02", id: "3"}, { date: "2014-10-03", id: "1"}, { date: "2014-10-01", id: "4"}, { date: "2014-10-02", id: "1"}, { date: "2014-10-01", id: "5"} }

I am trying to get the number of unique id's per date from this. I would like to group by date and basically have a count of unique id's for that particular date:

"2014-10-01" - 5 "2014-10-02" - 3 "2014-10-03" - 2 "2014-10-04" - 1 "2014-10-05" - 1

Currently, I'm trying to follow the answer given in this question

Crossfilter reduce :: find number of uniques

to do the following:

//Create a Crossfilter instance var ndx = crossfilter(va); //Define dimensions var date_dim = ndx.dimension(function(d) { return d["date"]; }); //total number of ids per date var num_ids_by_date = date_dim.group(); //unique number of ids per date var num_uniq_ids_by_date = date_dim .group() .reduce( function (p, d) { if(d.id in p.ids){ } else{ p.ids[d.id] = 1; } return p; }, function (p, d) { p.ids[d.id]--; if(p.ids[d.id] === 0){ delete p.ids[d.id]; } return p; }, function () { return {ids: {}}; })

When I look in the num_uniq_ids_by_date object and call num_uniq_ids_by_date.reduceCount().top(1), it seems to be the same output as num_ids_by_date.top(1).

So, I still don't seem to be getting what I'm looking for and have been stumped for a while.

Any suggestions? Thanks in advance!

Seems like you aren't incrementing the counter on add, which will cause you problems. If you put together a working example, it will be easier to diagnose the issue. You could also use a library like Reductio, which supports this: github.com/esjewett/… (plugging my own library, sorry) — Ethan Jewett
– Ethan Jewett, Commented Jul 28, 2015 at 21:03
Thanks for the response Ethan. The reason I don't increment the counter on add is because I don't entirely care about the amount of each particular id, I just would like the number of unique ids. Also, thanks for the library suggestion, I'll definitely check it out. If possible, I would like to keep it to just the CrossFilter library for now while I'm still learning :) — archeezee
– archeezee, Commented Jul 28, 2015 at 21:51
If you don't increment on add, but you decrement on remove (which you're doing), you're going to get into an inconsistent state pretty fast. I didn't see your actual question though. Calling num_uniq_ids_by_date.reduceCount() wipes out all your custom group reducers. Just call num_uniq_ids_by_date.top(1). — Ethan Jewett
– Ethan Jewett, Commented Jul 29, 2015 at 1:35
Oops, that was a mistake on my part - thanks for pointing it out. Thanks for the suggestions! I was actually able to get it. I'll be sure to add my answer. — archeezee
– archeezee, Commented Jul 29, 2015 at 19:36

archeezee · Accepted Answer · 2015-07-29 19:45:19Z

Okay I was able to get it.

What I ended up doing is the following:

//Create a Crossfilter instance var ndx = crossfilter(va); //Define dimensions var date_dim = ndx.dimension(function(d) { return d["date"]; }); var num_unique_ids_by_date = date_dim .group() .reduce( function (p, d) { if(d.id in p.ids){ p.ids[d.id] += 1 } else{ p.ids[d.id] = 1; p.id_count++; } return p; }, function (p, d) { p.ids[d.id]--; if(p.ids[d.id] === 0){ delete p.ids[d.id]; p.id_count--; } return p; }, function () { return {ids: {}, id_count: 0}; });

This gives me a total number of unique id's as well as the total numer of occurences of each id.

Then when I want to display this in my bar graph using dc.js, I go ahead and use the following code.

var minDate = date_dim.bottom(1)[0]["date"]; var maxDate = date_dim.top(1)[0]["date"]; var timeChart = dc.barChart("#time-chart"); timeChart .width(1500) .height(400) .margins({top: 10, right: 50, bottom: 30, left: 50}) .dimension(date_dim) .group(num_unique_ids_by_date) .valueAccessor(function (d) { return d.value.id_count; }) .transitionDuration(500) .x(d3.time.scale().domain([minDate, maxDate])) .elasticY(true) .elasticX(true) .xAxisLabel("Year") .yAxis(); dc.renderAll();

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