Max and min from QVector<QPoint>

[awpitt13]

Hello,

I have an array of QVector <QPoint> and I'm trying to find the maximum and minimum of each x and y. (trying to get X max, X min, Y max, Y min). Is there a clean way of going about this? I was looking at QSort but I'm not sure how to seperate the QPoint container into its x and y.

Thank you in advance for any advice you can offer.

[norobro]

See the overloaded qSort function here. You will obviously have to sort twice so you need to define one function comparing the x values and another comparing the y values.

[ChrisW67]

Here are two other options:

#include <limits>
 
QVector<QPoint> array;
array << QPoint(-1, 5) << QPoint(-2, 0) << QPoint(0, 3);
 
Q_ASSERT(array.size() > 0);
int xMin = std::numeric_limits<int>::max(); // everything is <= this
int xMax = std::numeric_limits<int>::min(); // everything is >= this
int yMin = std::numeric_limits<int>::max();
int yMax = std::numeric_limits<int>::min();
foreach (QPoint p, array) {
    xMin = qMin(xMin, p.x());
    xMax = qMax(xMax, p.x());
    yMin = qMin(yMin, p.y());
    yMax = qMax(yMax, p.y());
}
qDebug() << xMin << xMax << yMin << yMax;

#include <limits>

QVector<QPoint> array;
array << QPoint(-1, 5) << QPoint(-2, 0) << QPoint(0, 3);

Q_ASSERT(array.size() > 0);
int xMin = std::numeric_limits<int>::max(); // everything is <= this
int xMax = std::numeric_limits<int>::min(); // everything is >= this
int yMin = std::numeric_limits<int>::max();
int yMax = std::numeric_limits<int>::min();
foreach (QPoint p, array) {
    xMin = qMin(xMin, p.x());
    xMax = qMax(xMax, p.x());
    yMin = qMin(yMin, p.y());
    yMax = qMax(yMax, p.y());
}
qDebug() << xMin << xMax << yMin << yMax;

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or

QPolygon poly(array);
QRect brect = poly.boundingRect();
 
qDebug() << brect.left()  << brect.right() << brect.top() << brect.bottom();  // note the smallest y is the top of the box not the bottom

QPolygon poly(array);
QRect brect = poly.boundingRect();

qDebug() << brect.left()  << brect.right() << brect.top() << brect.bottom();  // note the smallest y is the top of the box not the bottom

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[norobro]

@ChrisW67: The QPolygon::boundingRect() solution is a good one. Hadn't thought of that.

@awpitt13: The qSort code:

#include <QtCore>
 
bool xLessThan(const QPoint &p1, const QPoint &p2){ return p1.x()<p2.x();}
 
bool yLessThan(const QPoint &p1, const QPoint &p2){  return p1.y()<p2.y();}
 
int main(){    
    srand(time(NULL));
    QVector<QPoint> vec;
    for(int i=0; i<5; i++)
        vec.append(QPoint(rand() % 100, rand() % 100));
    qDebug() << vec;
    qSort(vec.begin(),vec.end(),xLessThan);
    qDebug() << "Min X=" << vec.first().x() <<"\tMax X="<< vec.last().x();
    qSort(vec.begin(),vec.end(),yLessThan);
    qDebug() << "Min Y="<< vec.first().y()<<"\tMax Y=" << vec.last().y();
    return 0;
}

#include <QtCore>

bool xLessThan(const QPoint &p1, const QPoint &p2){ return p1.x()<p2.x();}

bool yLessThan(const QPoint &p1, const QPoint &p2){  return p1.y()<p2.y();}

int main(){    
    srand(time(NULL));
    QVector<QPoint> vec;
    for(int i=0; i<5; i++)
        vec.append(QPoint(rand() % 100, rand() % 100));
    qDebug() << vec;
    qSort(vec.begin(),vec.end(),xLessThan);
    qDebug() << "Min X=" << vec.first().x() <<"\tMax X="<< vec.last().x();
    qSort(vec.begin(),vec.end(),yLessThan);
    qDebug() << "Min Y="<< vec.first().y()<<"\tMax Y=" << vec.last().y();
    return 0;
}

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[ChrisW67]

I expect that a bounding box is what awpitt13 is ultimately trying to determine.