@d3fc/d3fc-sample/test/modeMedianSpec.js

A data subsampler that chooses representative data points using a largest triangle or mode-median approach.

import modeMedian from '../src/modeMedian';

describe('modeMedian', function() {

    var data;
    var bucketGenerator;

    describe('simple data', function() {

        beforeEach(function() {
            data = [0, 1, 6, 4, 8, 4, 8, 9, 3, 5, 2, 10, 2, 4, 3, 8, 5];
            bucketGenerator = modeMedian()
                                .value(function(d) { return d; });
        });

        it('should return original data if the number of buckets is longer than the data', function() {
            expect(bucketGenerator.bucketSize(100)(data))
                .toEqual(data);
        });

        it('should return the correct number of buckets if summarisation occurs', function() {
            var subsampledData = bucketGenerator.bucketSize(5)(data);
            expect(subsampledData).toHaveLength(5);
        });

        it('should have the first and last buckets be the first and last data points', function() {
            var subsampledData = bucketGenerator.bucketSize(5)(data);
            expect(subsampledData[0]).toEqual(0);
            expect(subsampledData[4]).toEqual(5);
        });

        it('should have 2 buckets with the global max and min', function() {
            var subsampledData = bucketGenerator.bucketSize(5)(data);
            expect(subsampledData[0]).toEqual(0);
            expect(subsampledData[3]).toEqual(10);
        });

        it('should return the most common number if there is one', function() {
            var subsampledData = bucketGenerator.bucketSize(5)(data);
            expect(subsampledData[1]).toEqual(4);
        });

        it('should return the middle data point if there is no mode', function() {
            var subsampledData = bucketGenerator.bucketSize(5)(data);
            expect(subsampledData[2]).toEqual(3);
        });
    });

    describe('array data', function() {
        beforeEach(function() {
            data = [[0, 1], [6, 4], [8, 4], [8, 9], [3, 0], [2, 10], [2, 4], [3, 8]];
            bucketGenerator = modeMedian()
                                .value(function(d) { return d[1]; });
        });

        it('should return a 2-dimensional array', function() {
            var subsampledData = bucketGenerator.bucketSize(6)(data);

            expect(subsampledData[0][1]).toEqual(1);
            expect(subsampledData[1][1]).toEqual(0);
            expect(subsampledData[2][1]).toEqual(8);
        });
    });
});