c3/docs/js/samples/data_stringx.js

var chart = c3.generate({
    data: {
        x : 'x',
        columns: [
            ['x', 'www.site1.com', 'www.site2.com', 'www.site3.com', 'www.site4.com'],
            ['download', 30, 200, 100, 400],
            ['loading', 90, 100, 140, 200],
        ],
        groups: [
            ['download', 'loading']
        ],
        type: 'bar'
    },
    axis: {
        x: {
            type: 'category' // this needed to load string x value
        }
    }
});

setTimeout(function () {
    chart.load({
        columns: [
            ['x', 'www.siteA.com', 'www.siteB.com', 'www.siteC.com', 'www.siteD.com'],
            ['download', 130, 200, 150, 350],
            ['loading', 190, 180, 190, 140],
        ],
    });
}, 1000);

setTimeout(function () {
    chart.load({
        columns: [
            ['x', 'www.siteE.com', 'www.siteF.com', 'www.siteG.com'],
            ['download', 30, 300, 200],
            ['loading', 90, 130, 240],
        ],
    });
}, 2000);

setTimeout(function () {
    chart.load({
        columns: [
            ['x', 'www.site1.com', 'www.site2.com', 'www.site3.com', 'www.site4.com'],
            ['download', 130, 300, 200, 470],
            ['loading', 190, 130, 240, 340],
        ],
    });
}, 3000);

setTimeout(function () {
    chart.load({
        columns: [
            ['download', 30, 30, 20, 170],
            ['loading', 90, 30, 40, 40],
        ],
    });
}, 4000);

setTimeout(function () {
    chart.load({
        url: '/data/c3_string_x.csv'
    });
}, 5000);