Missing Data Points

This example demonstrates various methods to representing missing data points. It also demonstrates automatic resizing of the plot area to fit the chart.

In ChartDirector, a data series may contain missing values, represented using the NoValue predefined constant. In a line layer, by default, a missing value is represented as a gap in the line. In other words, the line will be broken. LineLayer.setGapColor can be used to configure the line layer to join through the NoValue point instead, using a line segment that can be of a different color and/or style.

In this example, the three data series all contain NoValue points. The red line demonstrates the default behaviour of using a gap to representing the NoValue point. The green line demonstrates joining through the NoValue point with a dash line. The orange line demonstrates joining through the NoValue point with the same line style as for joining normal data points.

After the entire chart is configured, the XYChart.packPlotArea method is used to adjust the plot area size, so as to fit the plot area and the axes in a given bounding box.

The following is the command line version of the code in "cppdemo/missingpoints". The MFC version of the code is in "mfcdemo/mfcdemo". The Qt Widgets version of the code is in "qtdemo/qtdemo". The QML/Qt Quick version of the code is in "qmldemo/qmldemo".

#include "chartdir.h"

int main(int argc, char *argv[])
{
    // The data for the chart
    double data0[] = {42, 49, Chart::NoValue, 38, 64, 56, 29, 41, 44, 57};
    const int data0_size = (int)(sizeof(data0)/sizeof(*data0));
    double data1[] = {65, 75, 47, 34, 42, 49, 73, Chart::NoValue, 90, 69, 66, 78};
    const int data1_size = (int)(sizeof(data1)/sizeof(*data1));
    double data2[] = {Chart::NoValue, Chart::NoValue, 25, 28, 38, 20, 22, Chart::NoValue, 25, 33,
        30, 24};
    const int data2_size = (int)(sizeof(data2)/sizeof(*data2));
    const char* labels[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct",
        "Nov", "Dec"};
    const int labels_size = (int)(sizeof(labels)/sizeof(*labels));

    // Create a XYChart object of size 600 x 360 pixels. Set background color to brushed silver,
    // with a 2 pixel 3D border. Use rounded corners.
    XYChart* c = new XYChart(600, 360, Chart::brushedSilverColor(), Chart::Transparent, 2);
    c->setRoundedFrame();

    // Add a title using 18pt Times New Roman Bold Italic font. #Set top/bottom margins to 6 pixels.
    TextBox* title = c->addTitle("Product Line Global Revenue", "Times New Roman Bold Italic", 18);
    title->setMargin(0, 0, 6, 6);

    // Add a separator line just under the title
    c->addLine(10, title->getHeight(), c->getWidth() - 11, title->getHeight(), Chart::LineColor);

    // Add a legend box where the top-center is anchored to the horizontal center of the chart, just
    // under the title. Use horizontal layout and 10 points Arial Bold font, and transparent
    // background and border.
    LegendBox* legendBox = c->addLegend(c->getWidth() / 2, title->getHeight(), false, "Arial Bold",
        10);
    legendBox->setAlignment(Chart::TopCenter);
    legendBox->setBackground(Chart::Transparent, Chart::Transparent);

    // Tentatively set the plotarea at (70, 75) and of 460 x 240 pixels in size. Use transparent
    // border and black (000000) grid lines
    c->setPlotArea(70, 75, 460, 240, -1, -1, Chart::Transparent, 0x000000, -1);

    // Set the x axis labels
    c->xAxis()->setLabels(StringArray(labels, labels_size));

    // Show the same scale on the left and right y-axes
    c->syncYAxis();

    // Set y-axis tick density to 30 pixels. ChartDirector auto-scaling will use this as the
    // guideline when putting ticks on the y-axis.
    c->yAxis()->setTickDensity(30);

    // Set all axes to transparent
    c->xAxis()->setColors(Chart::Transparent);
    c->yAxis()->setColors(Chart::Transparent);
    c->yAxis2()->setColors(Chart::Transparent);

    // Set the x-axis margins to 15 pixels, so that the horizontal grid lines can extend beyond the
    // leftmost and rightmost vertical grid lines
    c->xAxis()->setMargin(15, 15);

    // Set axis label style to 8pt Arial Bold
    c->xAxis()->setLabelStyle("Arial Bold", 8);
    c->yAxis()->setLabelStyle("Arial Bold", 8);
    c->yAxis2()->setLabelStyle("Arial Bold", 8);

    // Add axis title using 10pt Arial Bold Italic font
    c->yAxis()->setTitle("Revenue in USD millions", "Arial Bold Italic", 10);
    c->yAxis2()->setTitle("Revenue in USD millions", "Arial Bold Italic", 10);

    // Add the first line. The missing data will be represented as gaps in the line (the default
    // behaviour)
    LineLayer* layer0 = c->addLineLayer();
    layer0->addDataSet(DoubleArray(data0, data0_size), 0xff0000, "Quantum Computer")->setDataSymbol(
        Chart::GlassSphere2Shape, 11);
    layer0->setLineWidth(3);

    // Add the second line. The missing data will be represented by using dash lines to bridge the
    // gap
    LineLayer* layer1 = c->addLineLayer();
    layer1->addDataSet(DoubleArray(data1, data1_size), 0x00ff00, "Atom Synthesizer")->setDataSymbol(
        Chart::GlassSphere2Shape, 11);
    layer1->setLineWidth(3);
    layer1->setGapColor(c->dashLineColor(0x00ff00));

    // Add the third line. The missing data will be ignored - just join the gap with the original
    // line style.
    LineLayer* layer2 = c->addLineLayer();
    layer2->addDataSet(DoubleArray(data2, data2_size), 0xff6600, "Proton Cannon")->setDataSymbol(
        Chart::GlassSphere2Shape, 11);
    layer2->setLineWidth(3);
    layer2->setGapColor(Chart::SameAsMainColor);

    // layout the legend so we can get the height of the legend box
    c->layoutLegend();

    // Adjust the plot area size, such that the bounding box (inclusive of axes) is 15 pixels from
    // the left edge, just under the legend box, 16 pixels from the right edge, and 25 pixels from
    // the bottom edge.
    c->packPlotArea(15, legendBox->getTopY() + legendBox->getHeight(), c->getWidth() - 16,
        c->getHeight() - 25);

    // Output the chart
    c->makeChart("missingpoints.jpg");

    //free up resources
    delete c;

    return 0;
}