Example (JKQTPlotter): Boxplots

This project (see boxplot demonstrates how to use JKQTPlotter to draw box plots using the classes JKQTPBoxplotVerticalGraph and JKQTPBoxplotHorizontalGraph.

Note that this example explains how to add boxplots to a graph by hand, i.e. by calculating all the statistical properties for the boxplots by hand. The internal JKQTPlotter Statistics Library offers methods to perform these calculations, which are explained in the tutorial Advanced 1-Dimensional Statistics with JKQTPDatastore in detail. Additional advanced styling of boxplots is covered by the example Styling different aspects of boxplots.

The source code of the main application is (see boxplot.cpp.

After adding all necessary data to the JKQTDatastore:

// 2. now we create data for the boxplots
QVector<double> POS, POSY, MEDIAN, MEAN, Q25, Q75, MIN, MAX;
POS    << 1   << 4   << 7   << 10;
POSY   << -1  << -2  << -3  << -4;
MIN    << 2   << 3   << 2.5 << 6;
Q25    << 4   << 4.5 << 5   << 7;
MEDIAN << 5   << 6   << 7   << 9;
MEAN   << 5.5 << 5.2 << 8   << 8;
Q75    << 6   << 7   << 9   << 11;
MAX    << 8   << 7.5 << 11  << 12;
 
// 3. make data available to JKQTPlotter by adding it to the internal datastore.
size_t columnPOS=ds->addCopiedColumn(POS, "POS");
size_t columnPOSY=ds->addCopiedColumn(POSY, "POSY");
size_t columnMIN=ds->addCopiedColumn(MIN, "MIN");
size_t columnQ25=ds->addCopiedColumn(Q25, "Q25");
size_t columnMEDIAN=ds->addCopiedColumn(MEDIAN, "MEDIAN");
size_t columnMEAN=ds->addCopiedColumn(MEAN, "MEAN");
size_t columnQ75=ds->addCopiedColumn(Q75, "Q75");
size_t columnMAX=ds->addCopiedColumn(MAX, "MAX");

... you can generate the JKQTPBoxplotVerticalGraph:

// 4. create a graph of vertical boxplots:
JKQTPBoxplotVerticalGraph* graph=new JKQTPBoxplotVerticalGraph(&plot);
graph->setPositionColumn(columnPOS);
graph->setMinColumn(columnMIN);
graph->setPercentile25Column(columnQ25);
graph->setMedianColumn(columnMEDIAN);
graph->setMeanColumn(columnMEAN);
graph->setPercentile75Column(columnQ75);
graph->setMaxColumn(columnMAX);
graph->setTitle("vertical Boxplots");

You can further style the plot by e.g. setting:

// 6.1 make fill collor a lighter shade of the outline color
graphh->setFillColor(graphh->getLineColor().lighter());
// 6.2 make whiskers dashed
graphh->setWhiskerLineStyle(Qt::DashLine);
graphh->setWhiskerLineColor(graphh->getLineColor().darker());
// 6.3 make whiskers caps solid and thick
graphh->setWhiskerCapLineStyle(Qt::SolidLine);
graphh->setWhiskerCapLineColor(graphh->getLineColor().darker());
graphh->setWhiskerCapLineWidth(graphh->getLineWidth()*2.5);
// 6.4 change mean symbol
graphh->setMeanSymbolType(JKQTPFilledStar);
graphh->setMeanFillColor(QColor("silver"));
// 6.5 change median line color
graphh->setMedianLineColor(QColor("darkgreen"));
// 6.6 change box width to 75% of distance
graphh->setBoxWidthRelative(0.75);

The result looks like this:

In addition to the simple box plots, the image above also shows outliers as small circles. these need to be drawn with a separate JKQTPXYLineGraph:

// add some outliers (as (x,y)-pairs)
QVector<double> OUTLIERSX, OUTLIERSY;
OUTLIERSX << 4 << 4   << 4   << 4 << 4      << 10 << 10 << 10   << 10 << 10   << 10   << 10;
OUTLIERSY << 1 << 0.5 << 1.3 << 8 << 8.1    << 5  << 4  << 12.2 << 13 << 12.5 << 13.5 << 13.1;
 
// 3. make data available to JKQTPlotter by adding it to the internal datastore.
...
size_t columnOUTLIERSX=ds->addCopiedColumn(OUTLIERSX, "OUTLIERSX");
size_t columnOUTLIERSY=ds->addCopiedColumn(OUTLIERSY, "OUTLIERSY");
 
// 4. create a graph of vertical boxplots:
...
 
// 5. outliers need to be drawn separately
JKQTPXYLineGraph* graphOutliers=new JKQTPXYLineGraph(&plot);
graphOutliers->setXColumn(columnOUTLIERSX);
graphOutliers->setYColumn(columnOUTLIERSY);
graphOutliers->setTitle("outliers");
// make the color a darker shade of the color of graph
graphOutliers->setColor(graph->getColor().darker());
graphOutliers->setFillColor(QColor("white"));
// draw outliers as small circles, without lines
graphOutliers->setSymbolType(JKQTPCircle);
graphOutliers->setDrawLine(false);
graphOutliers->setSymbolSize(7);