Example (JKQTPlotter): Barchart With Error Bars

This project (see barchart_errorbars shows how to draw barcharts with different styles of error indicators.

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

// 1. create a plotter window and get a pointer to the internal datastore (for convenience)
JKQTPDatastore* ds=plot.getDatastore();
 
// 2. now we create three columns for key and value
size_t columnK=ds->addLinearColumn(6, 0.4*JKQTPSTATISTICS_PI, 2.2*JKQTPSTATISTICS_PI,"k");
size_t columnV=ds->addColumnCalculatedFromColumn(columnK, &cos, "v");
size_t columnE=ds->addColumnCalculatedFromColumn(columnK, [](double x) { return 0.05+0.06*(1.0+sin(x)); }, "error");
 
// 3. create a graph in the plot, which plots the dataset with symmetric:
JKQTPBarVerticalErrorGraph* graph1=new JKQTPBarVerticalErrorGraph(&plot);
graph1->setKeyColumn(columnK);
graph1->setValueColumn(columnV);
graph1->setBarErrorColumn(columnE);
// set error indicator style
graph1->setBarErrorStyle(JKQTPErrorBars);
graph1->setTitle(QObject::tr("JKQTPErrorBars"));
plot.addGraph(graph1);
 
// 4. create a second graph in the plot, which plots the second dataset with outer error bars only:
JKQTPBarVerticalErrorGraph* graph2=new JKQTPBarVerticalErrorGraph(&plot);
graph2->setKeyColumn(columnK);
graph2->setValueColumn(columnV);
graph2->setBarErrorColumn(columnE);
// set error indicator style
graph2->setBarErrorStyle(JKQTPErrorHalfBarsOutwards);
graph2->setTitle(QObject::tr("JKQTPErrorHalfBarsOutwards"));
plot.addGraph(graph2);
 
// 5. now we set the graphs, so they are plotted side-by-side
//    This function searches all JKQTPBarHorizontalGraph in the current
//    plot and sets their shift/scale so they form a nice plot with
//    side-by-side groups
graph1->autoscaleBarWidthAndShift(0.9, 0.9);
 
 
// 6 autoscale the plot so the graph is contained
plot.zoomToFit();
 
// 7. show plotter and make it a decent size
plot.getPlotter()->setKeyPosition(JKQTPKeyInsideTopLeft);
plot.setWindowTitle(title);
plot.show();
plot.resize(400,400);

The result looks like this:

In order to draw horizontal error bars, you have to use JKQTPBarHorizontalErrorGraph instead of JKQTPBarVerticalErrorGraph: