How can I force a dual y axis graph to use the same baseline for each axis?

Question

I have a Google Combination Chart where I am using two y axes.

At present, the baselines for each axis are at a different level.

I wish to ensure that the baselines for each axis are at the same level.

The code I am currently using to display my graph is shown below:

<html>
<head>
    <script type="text/javascript" src="https://www.google.com/jsapi"></script>
    <script>

    google.load("visualization", "1", {packages:["corechart"]});
    google.setOnLoadCallback(drawChart);
    function drawChart() {

    var data = new google.visualization.DataTable();

        data.addColumn('number', 'Sales');
        data.addColumn('number', 'Total PnL');
        data.addColumn('number', 'Total Margin');

        data.addRows([  [6.5,150.6,0.6604],
                        [7.0,-275,-1],
                        [7.5,-128.45000,-0.30368],
                        [8.0,345.5,0.63904761],
                        [8.5,-316.56000,-0.07868],
                        [9.0,-118.26000,-0.09587],
                        [9.5,-899.0699,-0.236790],
                        [10.0,-242.6800,-0.40805],
                        [10.5,28.1700,0.00786]  ]);                    

        var options = {
            title: 'Graph 1',
            tooltip: {textStyle: {fontSize:14}},
            titleTextStyle:{fontSize:12},
            hAxis: {title: 'time', titleTextStyle: {color: 'red',fontSize:15}, textStyle: {fontSize:11,fontStyle:'bold'}},
            legend: {maxLines:5,textStyle: {fontSize: 11.5}},
            seriesType: "bars",
            series: {
                    0: {type: "bar",targetAxisIndex:0,color:'#000000'},
                    1: {type: "line",targetAxisIndex:1,color:'#333333'},
                    }, 
            vAxes:{
                0:{title:'PnL',titleTextStyle: {fontSize:14},textStyle:{color: 'blue',fontSize:15},format:'£###,###,###'},
                1:{title:'Margin',titleTextStyle: {fontSize:14},textStyle:{color: 'red',fontSize:15},format:'#.###%'}
                }
        };      

      var chart = new google.visualization.ComboChart(document.getElementById('graphdiv'));
      chart.draw(data, options);
    }

    </script>
</head>
<body>
    <div id='graphdiv' style='width: 900px; height: 500px;'></div>
</body>
</html>

I am aware of the following two questions on stackoverflow that are relevant to this question:

It seems to me that the first of these deals specifically with the situation where the data is known beforehand. It would also be useful to see some indication of the javascript required to implement it.

The second provides some useful javascript, but it cannot seem to deal with data series where the second series includes negative values, as my dataset does.

I am aware that the most important component of both of these answers is making use of the minValue and maxValue properties of each of the vAxes. Changing these can be used to override the way that Google Charts typically decides the baseline for each axis (usually it does this by looking purely at the minimum and maximum values of the data itself for each individual axis).

score 2 · Accepted Answer · answered Feb 12 '15 at 20:42

I found an answer to the question above on the google visualisation api discussion group, courtesy of @asgallant. See here.

I have reproduced the answer below:

If having the baseline always be in the center of the chart is acceptable (even when there are no data points below it), there is an easy solution to this problem: get the min/max for each series and set the minValue/maxValue options to the negative of the opposite value: this will ensure that the actual min/max that the chart uses to determine the axis range is symmetrical around 0, and thus both axes should share a baseline at the center of the chart.

var axis0Range = data.getColumnRange(1);

var axis1Range = data.getColumnRange(2);

in the vAxes option:

vAxes:{

0:{
    title:'PnL',
    titleTextStyle: {fontSize:14},
    textStyle:{color: 'blue',fontSize:15},
    format:'£###,###,###',
    // swap the min/max and multiply by -1
    minValue: axis0Range.max * -1,
    maxValue: axis0Range.min * -1
},
1:{
    title:'Margin',
    titleTextStyle: {fontSize:14},
    textStyle:{color: 'red',fontSize:15},
    format:'#.###%',
    // swap the min/max and multiply by -1
    minValue: axis1Range.max * -1,
    maxValue: axis1Range.min * -1
 }
}

How can I force a dual y axis graph to use the same baseline for each axis?

1 Answers1