How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot

[JonB]

@Raphawel
OK, so although you have not said I guess ui->customplot->graph(0) must be a QCPGraph?

Given the error message tells you what the issue is I don't know what further to say. You are passing QCPGraph::setData() two QStringLists, list of strings, and not surprisingly it does not accept those. So look at QCPGraph::setData() documentation to see what it does accept.

[Raphawel]

@jsulm Yes the message tells me that I need QVectors inside setData() :

void QCPGraph::setData ( const QVector< double > &  keys, const QVector< double > &  values, bool  alreadySorted = false  )

So I readapted:

lineList.append(champs[0]);
            columnList.append(champs[1]);

            QVector<double> xData2 = lineList;
            QVector<double> yData2 = columnList;
            ui->customplot->graph(0)->setData(xData2, yData2);
            ui->customplot->replot();

But I still have errors due to a conversion problem:

C:\Users\46053500\Documents\Graph_QT\graphConso\graphconso.cpp:123: erreur : conversion from 'QStringList' to non-scalar type 'QVector<double>' requested
             QVector<double> xData2 = lineList;
                                      ^

C:\Users\46053500\Documents\Graph_QT\graphConso\graphconso.cpp:124: erreur : conversion from 'QStringList' to non-scalar type 'QVector<double>' requested
             QVector<double> yData2 = columnList;
                                      ^

I'm sorry if the errors are really glaring but I really don't see how to solve them

[SimonSchroeder]

@Raphawel You need to transform all entries inside the lists individually. For example, you could use lineList[0].toDouble() to convert a single QString to a double value. There is not automatic conversion from strings to numbers. In imperative programming a for loop comes to mind. However, here is a more functional style approach to "copy" the data over using standard C++:

QVector<double> xData2;
std::transform(lineList.begin(), lineList.end(), std::back_inserter(xData2), [](const QString &str) { return str.toDouble(); });

[Raphawel]

@SimonSchroeder

        QStringList lineList = {};
        QStringList columnList = {};
        QVector<double> xData2;
        QVector<double> yData2;

        while(!flux.atEnd())
        {
            QString ligne = flux.readLine();
            QStringList champs = ligne.split(";", QString::KeepEmptyParts); //::KeepEmptyParts : Permet de voir les zones vides et de noter les résultats que quand il y en a

            lineList.append(champs[0]);
            columnList.append(champs[1]);

            xData2.append(champs[0].toDouble());
            yData2.append(champs[1].toDouble());
            
            ui->customplot->graph(0)->setData(xData2, yData2);
            ui->customplot->replot();

I tried to do a QString to double conversion my way. And the program compiles well. And I have the impression that it did the conversion well. Except that I have an error that appears after compilation :

Already if the help you gave me doesn't correspond at all to what I just did, can you tell me please ?

And what does this message mean : The inferior stopped because it received a signal from the operating system

[jsulm]

@Raphawel said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

lineList.append(champs[0]);
columnList.append(champs[1]);

You're not checking how many elements the list actually contains!
Also, take a look at the stack trace: it tells where in your code it crashes.

[JonB]

@Raphawel

1. Make sure that the ligne.split() always returns (at least) 2 elements.
2. Check the result from champs[0].toDouble() (hint: it takes an optional bool *ok = nullptr parameter). Since I see your column #0 seems to contain date string how do you expect them to convert to a double?
3. I don't think this is required, but does it make any difference if you make x/yData2 vectors have lifetime scope outside the code you show, e.g. as class member variables? [Having said that I suspect the setData(xData2, yData2) takes a copy anyway?
4. Make sure your graph(0) does point to a valid QCPGraph and that starts out empty.
5. Try a clearData() before calling setData() each time.

The first thing to check is #2 (and of course #1).

[Raphawel]

@JonB Thank you very much for detailing the steps to follow :) Considering my level, I tried to reproduce what is asked:

1. For lineindex = 0 :

QStringList champs = ligne.split(";", QString::KeepEmptyParts); return 4 éléments :
champs[0] = "09/21/2022 02:30 PM CEST"
champs[1] = ""
champs[2] = ""
champs[3] = "576"

2. For lineindex = 0 :
   lineList.append(champs[0]); -> return "09/21/2022 02:30 ..." -> type QString
   columnList.append(champs[1]); -> return "" -> type QString
   xData2.append(champs[0].toDouble()); -> return "0" -> type double
   yData2.append(champs[1].toDouble()); -> return "0" - > type double

   xData2 and yData2-> Type QVector <double>

For lineindex = 1 :
lineList.append(champs[0]); -> return "09/21/2022 02:45 ..." -> type QString
columnList.append(champs[1]); -> return "2.712" -> type QString
xData2.append(champs[0].toDouble()); -> return "0" -> type double
yData2.append(champs[1].toDouble()); -> return "0" - > type double

But I see that yData2 doesn't understand float values when it is a double when for example :

columnlist[1] = 2.712 then yData2[1] = 0

But that it understands the integer values:

columnlist[3] = 240 then yData[3] = 240.

On the other hand, I have to find a way to do the conversion of a QString for xData

3. It does not change anything

4. I am blind, I forgot to add :

ui->customplot->addGraph();

5. I added it

So, this time I removed this error : https://forum.qt.io/post/749704 as I can access my graph.

[jsulm]

@Raphawel said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

lineList.append(champs[0]); -> return "09/21/2022 02:30 ..." -> type QString
columnList.append(champs[1]); -> return "" -> type QString
xData2.append(champs[0].toDouble()); -> return "0" -> type double
yData2.append(champs[1].toDouble()); -> return "0" - > type double

Neither "09/21/2022 02:30 ..." nor "" empty string can be converted to a double...

[SimonSchroeder]

Most likely the reason for your crash is that there is an extra empty line at the end of the file. You are trying to convert that as well. Hence why you need to check if there are enough items.

It is not surprising that a date cannot be converted to a double. Does QCustomPlot support dates? Otherwise you need to use QDateTime to convert the string to a date and use one of its functions to convert it to milliseconds from a specific date (most likely the first date you have) and assign the milliseconds to the double vector (maybe convert them to days instead).

Concerning the second column: Do you get numbers like 2.712 or 2,712? Which is the string you read from the .csv file? The screenshot is telling a different story than your text. Most likely this is related to the locale that is used.

[Raphawel]

@SimonSchroeder The string I changed the number of lines to look at (30).
So the values of the 1st column are only in the form: "MM/dd/yyyy hh:mm AP".

The string I get back is : "MM/dd/yyyy hh:mm AP" for lineList

For xData2:
Before my while it is defined as a

QVector<double> xData2;

In the while I convert it with

xData2.append(QDateTime::fromString(fields[0], "hh:mm").toTime_t())

I understood that we can't convert a string to a double but the problem is that setData only accepts QVector<double>, why ???

And whatever the type I put (not double) I have all the time the same errors

C:\Users\46053500\Documents\Graph_QT\graphConso\graphconso.cpp:140: error : no matching function for call to 'QCPGraph::setData(QVector<char>&, QVector<double>&)'
         ui->customplot->graph(0)->setData(xData2, yData2);
                                                         ^

My questions: is there a simple way to display a string like mine "MM/dd/yyyy hh:mm AP" on the x axis and an integer(power) on the Y axis.

So by having : setData(QString, double). Despite the fact that setData doesn't accept anything aside doubles

So the conversion method you just proposed @SimonSChroeder. I tried to do it:
```
QStringList lineList = {};
QStringList columnList = {};
QVector<double> xData2;
QVector<double> yData2;
QDateTime referenceDateTime;

    while(lineindex<30)
    {
        QString ligne = flux.readLine();
        QStringList champs = ligne.split(";", QString::KeepEmptyParts); //::KeepEmptyParts : Permet de voir les zones vides et de noter les résultats que quand il y en a


        lineList.append(champs[0]);
        columnList.append(champs[1]);

        if(lineindex==0)
        {
            referenceDateTime = QDateTime::fromString(lineList,"MM/dd/yyyy hh:mm AP");
        }

        QDateTime dateTime = QDateTime::fromString(champs[0],"MM/dd/yyyy hh:mm AP");

        qint64 milliseconds = dateTime.toMSecsSinceEpoch() - referenceDateTime.toMSecsSinceEpoch();
        xData2.append(milliseconds); // "MM/dd/yyyy hh:mm AP"
        yData2.append(champs[1].toDouble());

        QString valueL = lineList[lineindex];
        QString valueC = columnList[lineindex];
        QStandardItem *itemL = new QStandardItem(valueL);
        QStandardItem *itemC = new QStandardItem(valueC);
        model->setItem(lineindex, 0,  itemL);
        model->setItem(lineindex, 1,  itemC);

        lineindex++;

    }

    file.close();

    ui->customplot->addGraph();
    ui->customplot->graph(0)->data()->clear();
    ui->customplot->graph(0)->setData(xData2, yData2);

But it doesn't work because of the same problem:

C:\Users\46053500\Documents\Graph_QT\graphConso\graphconso.cpp:125: error : no matching function for call to 'QDateTime::fromString(QStringList&, const char [20])'
                 referenceDateTime = QDateTime::fromString(lineList, "MM/dd/yyyy hh:mm AP");
                                                                                         ^

"Do you get numbers like 2.712 or 2,712?" For the 2nd column, I get values 2,712

[jsulm]

@Raphawel said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

setData only accepts QVector<double>, why ???

Because it plots vectors of doubles.

"I understood that we can't convert a string to a double" - this is wrong. You can convert a string to double if the string contains valid text representation of a number.
""09/21/2022 02:30" - this is NOT a double!

[Raphawel]

@jsulm said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

Because it plots vectors of doubles.
"I understood that we can't convert a string to a double" - this is wrong. You can convert a string to double if the string contains valid text representation of a number.
""09/21/2022 02:30" - this is NOT a double!

"09/21/2022 02:30" I get that. So I have to convert it using @SimonSChroeder's method to hope to display it.
Why is it not as easy as in Excel to display the x axis with dates like this....

And also aren't there vector plots of QString?

[jsulm]

@Raphawel said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

And also aren't there vector plots of QString?

Why don't you read QCustomPlot documentation? It is not part of Qt.
So, if you read their documentation you will find this: https://www.qcustomplot.com/index.php/tutorials/basicplotting scroll down to "Plotting date and time data"...

[SimonSchroeder]

You need to learn to read error messages more thoroughly.

@Raphawel said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

C:\Users\46053500\Documents\Graph_QT\graphConso\graphconso.cpp:140: error : no matching function for call to 'QCPGraph::setData(QVector<char>&, QVector<double>&)'
ui->customplot->graph(0)->setData(xData2, yData2);
This error message tells you that the first parameter you are handing in is of type QVector<char>. By now we have established that it should be QVector<double>. You should be able to figure out that you are passing the wrong variable here.

@Raphawel said in How to retrieve data from an excel .csv file, and put it in a graph with QCustomPlot:

C:\Users\46053500\Documents\Graph_QT\graphConso\graphconso.cpp:125: error : no matching function for call to 'QDateTime::fromString(QStringList&, const char [20])'
referenceDateTime = QDateTime::fromString(lineList, "MM/dd/yyyy hh:mm AP");
And again it tells you that the type of the first parameter is QStringList. As the function name implies it wants a QString instead. So, you need to take one element out of the string list to pass to the function.

Please have a careful look at the error messages because these ones you are posting are really easy to read and see what's wrong. C++ is a strongly typed language. Learn to use this power to your advantage. The compiler exactly tells you when you are using the wrong type. And it is a lot better to have this information at compile time than to have to figure this out at runtime.