Read data and add it to a chart

[JonB]

@suslucoder
@jsulm already answered this last question in https://forum.qt.io/topic/122320/how-can-i-add-txt-file-datas-in-qlineseries/2. You cannot add a a string (or string list) to a chart, you have to parse it to generate the actual desired numbers.

For adding data every few seconds: whether you read the lines from the file as you go or you read them all into a list in memory, either way on a QTimer::timeout() signal read the next however-many from the file/list and add them to the chart.

[deleted286]

@JonB Okey. I understand. I should use another struct instead of string list, right?

[JonB]

@suslucoder
Well it's not another "struct". You presumably have a file containing the text of numbers, perhaps separated by commas or new lines or something. You need to convert those to X,Y numeric values, and then pass those (or QPointFs) to add to the chart series. It doesn't matter whether you do that at the time of reading in the file or just before adding them to the series, but you will need to do so at one of those two stages.

[jsulm]

@suslucoder said in Read data and add it to a chart:

I should use another struct instead of string list, right?

You should use what the method to set the data expects. That's why I suggested to read the documentation: it is documented quite clearly.

[deleted286]

@jsulm ıs there any example that doing exactly what you said?

[jsulm]

@suslucoder I already posted a link to charts examples.
For example: https://doc.qt.io/qt-5/qtcharts-temperaturerecords-example.html
And you still did not tell us what data you actually want to show and what type of chart you need...

[mrjj]

Hi
Please show one line from the "C:/Users/ilknu/Documents/QFileDemo/abc.txt"
so we know how data is. else it's impossible to give any hints on how you can show that in a chart.

[deleted286]

@mrjj Here it is

1991 01 213.5 136.9 0.64 220.5 147.6 229.4 205.5 8 17.4
1991 02 270.2 167.5 0.62 221.5 147.6 243.0 206.3 10 18.4

[JonB]

@suslucoder

QString line = read_one_line_from_file();
QStringList list = line.split(QLatin1Char(' '), Qt::SkipEmptyParts);
for (const QString &entry : list)
{
    double num = entry.toDouble();    // or `unsigned num = entry.toUInt()` for the first 2 numbers on each line, by the look of it
    // do whatever is necessary with each `double` number retrieved
    // such as adding pairs directly to the chart, or building a `QLineSeries`, or whatever
}

[deleted286]

@JonB Thank you. Where should I place the code script?

[jsulm]

@suslucoder said in Read data and add it to a chart:

Where should I place the code script?

Come on. Place is where you read the data from the file...

[deleted286]

@jsulm I know but i have, QString line = in.readLine();
allLines.append(line);
I couldnt get the idea about it. When i do it i get out of index error .And after doing all this things, how can i add my datas to a chart?

[deleted286]

@suslucoder I did this part. After that, how can i add it to a chart? Like the way create a new chart, append series and it goes like this?

[jsulm]

@suslucoder said in Read data and add it to a chart:

And after doing all this things, how can i add my datas to a chart?

I already provided links to examples several times.

"When i do it i get out of index error" - then post your code...

[deleted286]

@jsulm ```
QString line = in.readLine();
allLines.append(line);
QStringList list = line.split(QLatin1Char(' '), Qt::SkipEmptyParts);
for(const QString &entry : list) {
double num = entry.toDouble();
}
series->append(num)
``
Says use of undeclared identifier num

[mrjj]

Hi
You want like

QStringList list = line.split(QLatin1Char(' '), Qt::SkipEmptyParts);
for(const QString &entry : list) {
double num = entry.toDouble();
series->append(X,Y);  // use num for either xor y or both depending on what you want
}

[SGaist]

@mrjj said in Read data and add it to a chart:

series->append(num); // add each number from the line

This cannot work as QLineSeries does not have such an overload.

Currently discussed here.

[mrjj]

@SGaist
Good catch.
yes its x,y.
It was more about num being undeclared at that point in time :)
Changed as not to confuse future readers.