movie/public/plugin/c3-0.7.20/docs/js/samples/axes_x_tick_count.js

var chart = c3.generate({
    data: {
        x: 'x',
        columns: [
            ['x', '2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06', '2013-01-07', '2013-01-08', '2013-01-09', '2013-01-10', '2013-01-11', '2013-01-12'],
            ['sample', 30, 200, 100, 400, 150, 250, 30, 200, 100, 400, 150, 250]
        ]
    },
    axis: {
        x: {
            type: 'timeseries',
            tick: {
                count: 4,
                format: '%Y-%m-%d'
            }
        }
    }
});