c3 js: How can I group by Year on the X-axis labels?

Question

Using c3 js library for charts (c3js.org). I'am trying to achieve something similar to this chart (i.e., add year label 2011, 2012, 2013 on a seperate line after Q1, Q2, Q3, Q4)

var chart = c3.generate({
data: {
    x: 'x',
    columns: [
        ['x', '2013-01-01', '2013-01-02', '2013-01-03', '2014-01-04', '2014-01-05', '2014-01-06'],
        ['data1', 30, 200, 100, 400, 150, 250],
        ['data2', 130, 340, 200, 500, 250, 350]
    ]
},
axis: {
    x: {
        type: 'timeseries',
        tick: {
            format: '%Y-%m-%d'
        }
    }
}
});

show's the x axis with year in each label in the format year-month-day. I want to show just the month and date on first line of label and the year in the next line (without repetition). Kind of like:

format: function(){
     var label = '%m-%d';
     if(year!written)
           label +='%Y';
     return label;
}

Answer 1

You can do this using the tick format to write the labels

...
tick: {
    culling: false,
    count: (x.length - 1) * 2 - 1,
    format: function (d) {
        // show the year in place of Jul
        if (d.getMonth() === 6)
            return d.getFullYear();
        // ignore other non quarter months
        else if ([1, 4, 7, 10].indexOf(d.getMonth()) === -1)
            return '';
        // quarter months
        else
            return 'Q' + parseInt(d.getMonth() / 3 + 1);
    }
}
...

where x is the date labels array

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Then using d3 to select and push the year labels a bit down

// push the years down
d3.selectAll('#chart .tick text tspan')[0].forEach(function (d) {
    var tspan = d3.select(d);
    if (!isNaN(Number(tspan.text())))
        tspan.attr('dy', '2em')
    else
        tspan.attr('dy', '0.5em')
})

where chart is the ID of the chart container

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And finally hiding all the tick marks (or you could use the CSS nth-of-type selector to hide / show the ones you don't want)

#chart .tick line {
    display:none;
}

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Fiddle - http://jsfiddle.net/rg082b19/

I'm having intermittent problems with the Fiddle not pushing the labels down when you Run, but that doesn't happen outside of the fiddle. So if you don't see the axis labels moving down, just copy the code into a local HTML file and it will work.

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