snapping brush to the next x value? [dc.js] - dc.js

Question

I have a line chart and data in the form
[{
time: "2016-4-29"
total: 23242
},
{
time: "2016-5-16
total: 3322
}
...
]
I'm trying to filter on the x-axis with the brush, however, since I don't have every single date, if I brush in a small range, the filter handler seems to return an empty array for my filters
I've set up my line chart's x-axis like so:
.x(d3.time.scale().domain([minDate,maxDate]))
is there a way to make it so a user can only filter on dates that are in the dataset?
I would like the brush to snap to dates in the dataset.
it seems like whats happening is that you are able to brush between ticks..so it doesn't know what it selected.

Answer 1

I'm going to answer the easier question: How do I create a brush that will not allow nothing to be selected?
In other words, if the brush contains no data, do not allow it to take.
There are two parts to the solution. First, since any chart with a brush will remove the old filter and then add the new filter, we can set up the addFilterHandler to reject any filter that does not contain non-zero bins:
spendHistChart.addFilterHandler(function(filters, filter) {
var binsIn = spendHistChart.group().all().filter(function(kv) {
return filter.isFiltered(kv.key) && kv.value;
});
console.log('non-empty bins in range', binsIn.length);
return binsIn.length ? [filter] : [];
});
That's the straightforward part, and incidentally I think you could probably modify it to snap the brush to existing data. (I haven't tried it, though.)
The more tricky part is that this won't get rid of the brush, it just doesn't apply the filter. So the chart will end up in an inconsistent state.
We need to detect when the brush action has finished, and if there is no filter at that point, explicitly tell the chart to clear the filter:
spendHistChart.brush().on('brushend.no-empty', function() {
if(!spendHistChart.filters().length)
window.setTimeout(function() {
spendHistChart.filterAll().redraw();
}, 100);
});
We need a brief delay here, because if we respond to brushend synchronously, the chart may still be responding to it, causing bickering and dissatisfaction.
As a bonus, you get kind of a "nah-ah" animation because of the unintentional remove-brush animation.
demo fiddle