How to filter in crossfilter by current date and yesterday's date? - dc.js

Question

I want to make a query in crossfilter to filter all data from today's date.
Example: I have this query:
var countPerDim2 = Dim2.filterExact("1.1.2018").group().reduceSum();
So crossfilter will filter data from 1.1.2018.
But I want crossfilter to automatically get the the current date.
My reason is that I want to draw two charts to compare them.
Like :
Chart 1 by Date 1.1.2018 and Chart 2 by Date 31.12.17
How can I get the filter by yesterday's date? Is there a function like datenow() for the current day and maybe datenow(-1) for yesterday's date?
Thank you and happy new year!

Answer 1

Today and yesterday
To answer your immediate question, JavaScript's new Date() will return the current time and date as a JavaScript Date object. Then you just need to convert the date object to a string to match your date format.
You can use d3.time.format to produce those strings. Looks like you would want something like
d3.time.format('%-d.%-m.%Y')
(or perhaps with m and d reversed - unclear from your example whether month or day comes first)
Yesterday is something like
var date = new Date();
date.setDate(date.getDate()-1);
See the JavaScript Date documentation for more details.
Comparing two days
However, I think you'll run into a more fundamental problem, which is that crossfilter doesn't have the concept of multiple filters, so it's hard to compare one date against another in side-by-side charts.
Off the top of my head, the best thing I can think of is to "freeze" a group using a fake group:
function freeze_group(group) {
var _all = group.all().slice();
return {
all: function() {
return _all;
}
};
}
You'd apply one date filter, then call
chart.group(freeze_group(group));
on the chart you want to have that date. Now it won't change when the filter changes, and you can apply the other date filter for other charts.