I am try to swap axis from example:

demoName = "Quadratic Demo"; // generate some data: QVector<double> x(101), y(101); // initialize with entries 0..100 for (int i=0; i<101; ++i) { x[i] = i/50.0 - 1; // x goes from -1 to 1 y[i] = x[i]*x[i]; // let's plot a quadratic function } // create graph and assign data to it: customPlot->addGraph(); customPlot->graph(0)->setData(y, x); // give the axes some labels: customPlot->yAxis->setLabel("x"); customPlot->xAxis->setLabel("y"); // set axes ranges, so we see all data: customPlot->yAxis->setRange(-1, 1); customPlot->xAxis->setRange(0, 1);

and get wrong output.

The reason for this maybe QMap, which internally used for store data.

This bug is in all versions of QCustomPlot. Please fix it...