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);