Heat map filtering

[dtfoster]

I've noticed that filtering in the new heat map chart type only changes the colouring of the boxes correctly when clicking on a box or axis label. When calling the filter method manually (heatmapChart.filter([1,1]) for example), all of the boxes are greyed out after the filter, even though the filtering of the data has been applied correctly.

I think the issue is that the hasFilter function isn't currently set up to deal with 2 element arrays as input, such as [1,1]. I suggest something like the following to fix the issue:

_chart.hasFilter = function (filter) {
    if (!arguments.length) return _filters.length > 0;
    if (filter instanceof Array){
        var out;
        out = false;
        _filters.forEach(function(x){
            if (x.isFiltered(filter)){
            out = true
            }
        })
        return out
    }else{
        return _filters.indexOf(filter) >= 0
    };
};

[gordonwoodhull]

Thanks for the report and possible fix!

Would you be willing to submit a PR with tests that fail before and succeed after your fix? The current tests are in spec/heatmap-spec.js.