How do I format my secondary axis line values as percent using Google Chart API JavaScript in ASP.NET project

Question

My chart consists of 2 stacked bars on the primary vertical axis and a line on the secondary axis. My secondary vAxis is formatted as % and displays as I want, however, the individual datapoints display as decimal values, i.e., -0.446, and what I would like is -44.6%.

JavaScript code

 <script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
 <script type="text/javascript">

     google.charts.load('current', { packages: ['corechart'] });
     google.charts.setOnLoadCallback(drawChart);

     function drawChart() {
         var data = new google.visualization.DataTable();

         var jsonList = @(Json.Serialize(Model.listAllAircraftChart))

         var title = 'Monthly Aircraft Transaction Trend';

         data.addColumn('string', 'Month');
         data.addColumn('number', '2024');
         data.addColumn('number', '2023');
         data.addColumn('number', '% Change');
         data.addRows(jsonList.map((p) => {
             return [p.yearMonth, p.year1top, p.year2bottom, p.year1percent];
         }));

         var view = new google.visualization.DataView(data);
         view.setColumns([0, 1,
             {
                 calc: "stringify",
                 sourceColumn: 1,
                 type: "string",
                 role: "annotation"
             },
             2,
             {
                 calc: "stringify",
                 sourceColumn: 2,
                 type: "string",
                 role: "annotation"
             },
             3,
             {
                 calc: "stringify",
                 sourceColumn: 3,
                 type: "string",
                 role: "annotation"
             }

         ]);
         var options = {
             title: title,
             titlePosition: 'out',
             isStacked: true,

             seriesType: "bars",
             vAxes: {
                 0: {
                     textPosition: 'out',
                     viewWindowMode: 'pretty',
                     viewWindow: { min: -750, max: 750 },
                     gridlines: { color: 'light-gray' },
                 },
                 1: {
                     textPosition: 'out',
                     viewWindow: { min: -1, max: 1 },
                     format: 'percent',
                     gridlines: { color: 'transparent' }
                 },
             },
             series: {
                 0: { targetAxisIndex: 0, color: 'blue'},
                 1: { targetAxisIndex: 0, color: 'gray' },
                 2: { targetAxisIndex: 1, color: 'red', type: 'line', lineWidth: 1, lineDashStyle: [4, 4], pointSize: 5 },
             },
             width: '100%',
             height: '300',

             legend: { position: 'top' },
             chartArea: {
                 height: '100%',
                 width: '100%',
                 top: 48,
                 left: 60,
                 right: 60,
                 bottom: 75
             },
             annotations: {
                 textStyle: {
                     color: 'black',
                     fontSize: 11,
                 },
                 alwaysOutside: true
             },
         }

         var chart = new google.visualization.ComboChart(document.getElementById('primaryCurrentYear'));
         chart.draw(view, options);

         document.getElementById('downloadimg').innerHTML = '<a download="google-chart-image" href="' + chart.getImageURI() +
             '"><button type="button" class="btn btn-outline-dark btn-sm opacity-25 ms-4 mb-3">Download Chart Image</button></a>';

         window.addEventListener('resize', drawChart, false);
     }
 </script>

I have tried researching similar charts and reviewed Google Charts API documentation, but I haven't been able to figure it out.

Answer 1

you can use Google Charts' NumberFormat class...

here, we provide a number pattern to the formatter: #,##0.0%

var formatter = new google.visualization.NumberFormat({
  pattern: '#,##0.0%'
});

after creating the number formatter, you can use the format method to format an entire data table column.

formatter.format(data, 3);  // <-- format % Change column

see following working snippet...

google.charts.load('current', {
  packages: ['corechart']
}).then(drawChart);

function drawChart() {
  var data = new google.visualization.DataTable();

  //var jsonList = @(Json.Serialize(Model.listAllAircraftChart))
  var jsonList = [
    {yearMonth: 'January', year1top: 141, year2bottom: -158, year1percent: -0.108},
    {yearMonth: 'February', year1top: 98, year2bottom: -77, year1percent: -0.446},
    {yearMonth: 'March', year1top: 0, year2bottom: -299, year1percent: -1},
    {yearMonth: 'April', year1top: 0, year2bottom: -219, year1percent: -1},
    {yearMonth: 'May', year1top: 0, year2bottom: -272, year1percent: -1}
  ];

  var title = 'Monthly Aircraft Transaction Trend';

  data.addColumn('string', 'Month');
  data.addColumn('number', '2024');
  data.addColumn('number', '2023');
  data.addColumn('number', '% Change');
  data.addRows(jsonList.map((p) => {
     return [p.yearMonth, p.year1top, p.year2bottom, p.year1percent];
  }));

  // format % Change column
  var formatter = new google.visualization.NumberFormat({
    pattern: '#,##0.0%'
  });
  formatter.format(data, 3);

  var view = new google.visualization.DataView(data);
  view.setColumns([0, 1,
     {
         calc: "stringify",
         sourceColumn: 1,
         type: "string",
         role: "annotation"
     },
     2,
     {
         calc: "stringify",
         sourceColumn: 2,
         type: "string",
         role: "annotation"
     },
     3,
     {
         calc: "stringify",
         sourceColumn: 3,
         type: "string",
         role: "annotation"
     }

  ]);
  var options = {
     title: title,
     titlePosition: 'out',
     isStacked: true,

     seriesType: "bars",
     vAxes: {
         0: {
             textPosition: 'out',
             viewWindowMode: 'pretty',
             viewWindow: { min: -750, max: 750 },
             gridlines: { color: 'light-gray' },
         },
         1: {
             textPosition: 'out',
             viewWindow: { min: -1, max: 1 },
             format: 'percent',
             gridlines: { color: 'transparent' }
         },
     },
     series: {
         0: { targetAxisIndex: 0, color: 'blue'},
         1: { targetAxisIndex: 0, color: 'gray' },
         2: { targetAxisIndex: 1, color: 'red', type: 'line', lineWidth: 1, lineDashStyle: [4, 4], pointSize: 5 },
     },
     width: '100%',
     height: '300',

     legend: { position: 'top' },
     chartArea: {
         height: '100%',
         width: '100%',
         top: 48,
         left: 60,
         right: 60,
         bottom: 75
     },
     annotations: {
         textStyle: {
             color: 'black',
             fontSize: 11,
         },
         alwaysOutside: true
     },
  }

  var chart = new google.visualization.ComboChart(document.getElementById('primaryCurrentYear'));

  google.visualization.events.addListener(chart, 'ready', function () {
    document.getElementById('downloading').innerHTML = '<a download="google-chart-image" href="' + chart.getImageURI() +
       '"><button type="button" class="btn btn-outline-dark btn-sm opacity-25 ms-4 mb-3">Download Chart Image</button></a>';
  });

  chart.draw(view, options);

  window.addEventListener('resize', drawChart, false);
}

<script src="https://www.gstatic.com/charts/loader.js"></script>
<div id="primaryCurrentYear"></div>
<div id="downloading"></div>

note: getImageURI is only available after the chart's 'ready' event has fired...