How do I ensure the baselines for a dual-axis chart match up with one another?

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bsp...@gmail.com

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Oct 8, 2014, 1:38:59 PM10/8/14
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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>


This produces the following graph:



































I am aware that making use of the minValue and maxValue properties of each of the vAxes could be one way of dealing with this situation. But I am not sure how exactly I might do so.

Also, are there any future plans to make this a simple matter of adding

baseline-equal:true

to the vAxes options?

I apologise if this is the incorrect forum in which to ask about this issue.

Andrew Gallant

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Oct 8, 2014, 8:55:40 PM10/8/14
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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
    }
}

bsp...@gmail.com

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Oct 9, 2014, 2:13:19 PM10/9/14
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Many thanks for your quick response to my question. Your solution does indeed do what I require.
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