QCharts - QLineSeries from independent X and Y arrays

ratovarius

Hi,
What's the best way to plot two arrays in a LineChart with QCharts , one versus the other,

#define SIZE 100
int xArray[SIZE];
int yArray[SIZE];

Do I have to create a list of QPoints manually from these arrays?
Is there any way to add xArray or yArray to QLineSeries without modifying the other?

dheerendra

You can apply some thing simple like follows

QLineSeries *series0 = new QLineSeries();

series0->append(0,6);
series0->append(2,4);

chart.addSeries(series0);
You don't have to create Points.

ratovarius

Thanks for your answer. I'd like to append to QLineSeries the X coordinates independent from the Y coordinates, in your exaplme something like,

QLineSeries *series0 = new QLineSeries();

int xArray[2] = {0, 2};
int yArray[2] = {6, 4};

series0->setXData(xArray);
series0->setYData(yArray);

I want the best way to change X or Y data without modifying the other.

VRonin

You can set all the points with one of the coordinates at 0 and then use replace()

for(int i : xArray)
series0->append(i,0);
Q_ASSERT(series0->count()>=std::extent<decltype(yArray)>::value);
for(int i=0;i<std::extent<decltype(yArray)>::value;++i)
series0->replace(i,series0->at(i).x(),yArray[i]);

ratovarius

@VRonin
Thanks! Thats a way, but what about performance?
I'd like a way to pass a pointer to the x or y data structure, instead of copying it.
I am migrating an application that used Qwt. That library had some functions meant for performance like,

series.setRawSamples(xData, yData, numData);
painter.drawSeries(&series, from, to);

I know it's a different library, but I need to plot data in an environment with constant change in X or Y data.
I tried to use a QVXYModelMapper but I didn't find a way to manage the X and Y data from the model in a independent way.

VRonin

if you can use QVXYModelMapper then it's already done. For example:

mapper is QVXYModelMapper
i is the index of the point you want to change the Y coordinate for
newY is the new value for Y

mapper.model()->setData(mapper.model()->index(i,mapper.yColumn()), newY);