Parse large text file

[VRonin]

Regular expression don't render very well in this forum, see https://pastebin.com/1rDXQtSL

Source of the regexp for the decimal number: https://www.regular-expressions.info/floatingpoint.html (this is also the answer to @JonB, I don't type, I copy and paste, typing is for smart people)

[JonB]

@VRonin How do you type in this answer so fast --- do you have it pre-prepared? :)

[SGaist]

Hi,

The expression you are looking for is "X(\\d+(?:\\.\\d+)?) Y(\\d+(?:\\.\\d+)?)".

You should rather do the rounding with the captured data otherwise you will lose precession.

You can use the QRegularExpression tool to test your expressions.

[edit: Fixed RE missing . escaping SGaist]

[ODБOï]

You are awesome guys, thank you so much for quick/complete answers

[SGaist]

@LeLev take a look again at the expression. I forgot to escape the .. Therefore the expression was "wrong" in the sense that it will also find values like X1231a212.

[ODБOï]

@SGaist got it, thank you!

[ODБOï]

Hi !
I have lot of troubles trying to use the tool @SGaist
suggested to me. I want to edit my QRegularExpression so it also can catch lines where there is only X or only Y

N9 G40 X411 Y7.62 // capture 
N3 G40 Y6000 // << capture this also
N1 G0 X411 Y7.52 // capture
N3 G40 X-6000 // << capture this also

// ...open file 
 const QRegularExpression regx("X([-+]?\\d*\\.?\\d+)\\s+Y([-+]?\\d*\\.?\\d+)");
    QTextStream in(&file);

    while(!in.atEnd()) {

        QString line = in.readLine();
        const QRegularExpressionMatch reMatch = regx.match(line);
        bool iok;
        if(reMatch.hasMatch()){

            double lx = reMatch.captured(1).toDouble();
            double ly = reMatch.captured(2).toDouble();

            qDebug()<<"X : " << lx << " ly" << ly;
      
//please tell me if there is a more efficient way to get maximum/minimum X  and  maximum/minimum Y in this file, 
            if(lx<minX)
                minX=lx;
            else if (lx>maxX) maxX=lx;

            if(ly<minY)
                minY=ly;
            else if (ly>maxY) maxY=ly;
        }
    }

My final aim is to get maximum x and y And minimum x and y in the whole file
Thank you

[kshegunov]

https://regex101.com/r/n42ANB/1

When and/or if you use it, you must escape it properly for C++.

[ODБOï]

@kshegunov hi
thak you.
i only doubled the " \ "s

// (X(-?\d+(?:\.\d+)?))?\s*(Y(-?\d+(?:\.\d+)?))? 
 const QRegularExpression regx("(X(-?\\d+(?:\\.\\d+)?))?\\s*(Y(-?\\d+(?:\\.\\d+)?))?");

I tested your exemple on regex101.com and it is doind what i need. But in My program i get Zeros only

[VRonin]

This post is deleted!

[SGaist]

Because you are using way more capturing groups than you need and are not handling the case where there's no capture which is allowed since you make the whole thing optional.

What about simplifying things a bit ?

const QRegularExpression rx ("(?:[XY](-?\\d+(?:\\.\\d+)?))");

while (!in.atEnd()) {
    QString line = in.readLine();
    QRegularExpressionMatchIterator iter = re.globalMatch(line);
    bool ok;
    while (iter.hasNext()) {
        QRegularExpressionMatch match = iter.next();
        double x_or_y = match.captured(1).toDouble(&ok);
        if (!ok) {
               qDebug() << "Failed to convert" << match.captured(1);
               continue;
        }
        if (match.captured(0).startsWith(QLatin1Char('X')) {
              minX = qmin(minX, x_or_y);
              maxX = qmax(maxX, x_or_y);
        } else {
              minY = qmin(minY, x_or_Y);
              maxY = qmax(maxY, x_or_y);
        }
}

[edit: fixed rx, escaping was missing SGaist]

[VRonin]

I'd use:

const QRegularExpression regx("(?:([XY])([-+]?\\d*\\.?\\d+))");
QTextStream in(&file);
while(!in.atEnd()) {
    QString line = in.readLine();
    QRegularExpressionMatchIterator iter = re.globalMatch(line);
    while (iter.hasNext()){
        const QRegularExpressionMatch reMatch = iter.next();
        if(reMatch.captured(1).compare(QLatin1String("X"),Qt::CaseInsensitive)==0){ // matched X
            const double lx = reMatch.captured(2).toDouble();
            qDebug()<<"X : " << lx;
            if(lx<minX)
                minX=lx;
            else if (lx>maxX)
                maxX=lx;
        }
        else {// matched Y
            const double ly = reMatch.captured(2).toDouble();
            qDebug() << " ly" << ly;
            if(ly<minY)
                minY=ly;
            else if (ly>maxY)
                maxY=ly;
        }
    }
}