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

[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.

[julie546]

@Pl45m4 @KroMignon yes I have checked I have the right values ​​now I have a graph but it is not the same that I do with the csv file, I cannot find the same graph, what do you think please ?

[KroMignon]

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

but it is not the same that I do with the csv file,

What do you mean with not the same?

[julie546]

@KroMignon this is what I found with qt

and this is what I have to find

despite I made qDebug () << x;
qDebug () << y;
and I found the same values with csv file

[julie546]

This post is deleted!

[mrjj]

@julie546
Hi
If you look closely they are the same.
Its just you are using QLineSeries which draws lines between the points so
that why it looks differernt.

Maybe the scatter type can be used
https://doc.qt.io/qt-5/qtcharts-scatterchart-example.html

instead of the LineSeries.