how i can identify and read the columns of a csv file ?

[julie546]

how i can identify and read the columns of a csv file ?
I managed to open the file and identify the first column by : QStringList coordXList;
while (!filelidar.atEnd()) {
QByteArray line = filelidar.readLine();
coordXList.append(line.split(';').first());
QStringList coordXList;
}

        qDebug() << coordXList;

and I couldn't find how I can identify and read and the other columns how can i do it please

[jsulm]

@julie546 said in how i can identify and read the columns of a csv file ?:

and I couldn't find how I can identify and read and the other columns how can i do it please

split() gives you a list where you can access elements by their index. So, what is exactly the problem?

[JonB]

@julie546
And additonal to @jsulm you are splitting on ;, normally a CSV file elements are separated by ,?

[J.Hilk]

@JonB said in how i can identify and read the columns of a csv file ?:

@julie546
And additonal to @jsulm you are splitting on ;, normally a CSV file elements are separated by ,?

the default depends on your region, really.
Some languages use , as decimal point, than its usually ; as a separator

[julie546]

@JonB @J-Hilk no for my case it is;
@jsulm I can only read the first column but I would need the 2nd and 3rd

[jsulm]

@julie546 said in how i can identify and read the columns of a csv file ?:

I can only read the first column but I would need the 2nd and 3rd

Then read them. What is the problem, really?

QStringList elements = line.split(';');
//elements[0] -> first element ("column")
//elements[1] -> second element
...

[JonB]

@J-Hilk said in how i can identify and read the columns of a csv file ?:

Some languages use , as decimal point, than its usually ; as a separator

Gosh, I didn't realize that (the changed separator, and the comma in numbers being what is in the file). So a CSV file containing only numbers, say, is not portable across regions? I assumed they would export/import locale-independent, like C locale. This is bad!

[KroMignon]

@julie546 said in how i can identify and read the columns of a csv file ?:

how i can identify and read the columns of a csv file ?

I would suggest you to give qtcsv a try.
This should simplify working with CSV files

[JonB]

@julie546
@KroMignon has just recommended using qtcsv. I recommended same yesterday in post https://forum.qt.io/topic/128052/read-csv-file-values-and-put-these-values-in-a-graph/4 where someone asked about parsing CSV files. have a look at that, there are also other suggestions from a stackoverflow post (https://stackoverflow.com/questions/27318631/parsing-through-a-csv-file-in-qt), depending on how complex your situation is.

[julie546]

@JonB @KroMignon @jsulm @J-Hilk

thank you for your answer I was able to solve the problem with
coordXList.append (line.split (','). at (0));
coordYList.append (line.split (','). at (1));
but I would like to put these values ​​in a curve using the Qchart
I tried with
QLineSeries * series = new QLineSeries ();
series-> append (coordXList, coordYList);
but I got an error : no matching membre function for call to append
can you help me please

[J.Hilk]

@julie546 said in how i can identify and read the columns of a csv file ?:

but I got an error : no matching membre function for call to append
can you help me please

of course,
QLineSeries has 3 overloads

• append(qreal , qreal )
• append(const QPointF &)
• append(const QList<QPointF> &)

non of those fit your append(Container<ofSomeType>, Container<ofSomeType>)

[julie546]

@J-Hilk so I can't display a graph from a csv file?

[KroMignon]

@julie546 said in how i can identify and read the columns of a csv file ?:

thank you for your answer I was able to solve the problem with
coordXList.append (line.split (','). at (0));
coordYList.append (line.split (','). at (1));

This is a dangerous and no effective way to do!
line.split(',') may return an empty QStringList, so line.split (','). at(0) will crash your application.
And why splitting twice?

I would do it like this:

const auto parts = line.split (',');
if(parts.size() >= 2)
{
    coordXList.append(parts.at(0));
    coordYList.append(parts.at(1));
}

but I would like to put these values ​​in a curve using the Qchart
I tried with
QLineSeries * series = new QLineSeries ();
series-> append (coordXList, coordYList);
but I got an error : no matching membre function for call to append
can you help me please

Have you read QLineSeries::append() documentation??
There is not overload for QLineSeries::append(QStringList, QStringList)!

[KroMignon]

@julie546 said in how i can identify and read the columns of a csv file ?:

so I can't display a graph from a csv file?

Why not?
You have to convert your value to a compatible type. That's all.

[J.Hilk]

@julie546 thats not how programming works.

I assume coordXList and coordYList are string lists ?

than you may, and I emphasise may, get away with:

QLineSeries * series = new QLineSeries ();
for(int i{0}, j{qMin(coordXList.size(), coordYList.size())}; i<j; i++){
      series-> append (coordXList.at(i).toFloat(), coordYList.at(i).toFloat());
}

[julie546]

@J-Hilk yes here is my output ("Y", "0.170138", "0.161089", "0.15901", "0.157898", "0.159706", "0.162481", "0.167204", "0.172876", "0.169802", "0.1677",.....................)
theres an error with series-> append (coordXList.at(i).toFloat(), coordYList.toFloat());
no member named toFloat in QStringList
@KroMignon @J-Hilk can you help me please I am a beginner c ++ I am a student in mechanics but I need qt for my end of study internship

[J.Hilk]

@julie546 said in how i can identify and read the columns of a csv file ?:

no member named toFloat in QStringList

typo on my side, fixed it, but you should be able to fix that as well

[KroMignon]

@julie546 said in how i can identify and read the columns of a csv file ?:

can you help me please I am a beginner c ++ I am a student in mechanics but I need qt for my end of study internship

We have all started as beginner. I have studied electronics, not informatics, so I understand well your problem ;)

The easiest way to create the QLineSeries, is to do it while parsing:

QLineSeries * series = new QLineSeries();
while (!filelidar.atEnd()) {
    QString line = filelidar.readLine();
    const auto parts = line.split (',');
    if(parts.size() >= 2)
    {
        bool ok;
        qreal x = parts.at(0).toFloat(&ok);
        if(!ok)
            continue;
        qreal y = parts.at(1).toFloat(&ok);
        if(!ok)
            continue;
       series->append(x, y);
    }
}

[julie546]

@KroMignon yes it's really difficult to work in a field that you don't study
thank you for your answer I tried like that but I still have an empty curve

if (!filelidar.open(QFile::ReadOnly | QFile::Text) ) {
qDebug() << "File not exists";
} else {

                   QLineSeries * series = new QLineSeries();
                           while (!filelidar.atEnd()) {
                               QString line = filelidar.readLine();
                               const auto parts = line.split (',');
                               if(parts.size() >= 2)
                               {
                                   bool ok;
                                   qreal x = parts.at(0).toFloat(&ok);
                                   if(!ok)
                                       continue;
                                   qreal y = parts.at(1).toFloat(&ok);
                                   if(!ok)
                                       continue;
                                  series->append(x, y);
                               }
                           }



                       QChart *chart = new QChart(); 
                       chart->legend()->hide();
                       chart->addSeries(series);
                       chart->createDefaultAxes();
                       chart->setTitle("Lidar tg15"); 

                       QChartView *chartView = new QChartView(chart);
                       chartView->setRenderHint(QPainter::Antialiasing);

                       QMainWindow window; 
                       window.setCentralWidget(chartView); 
                       window.resize(1000, 1000); 
                       window.show(); /

}
}

[Pl45m4]

@julie546 said in how i can identify and read the columns of a csv file ?:

qreal x = parts.at(0).toFloat(&ok);
if(!ok)
continue;
qreal y = parts.at(1).toFloat(&ok);

Print the values for x and y and check if these are the values from your file.
The code from @KroMignon doesn't look wrong.