Converting QList<QString> to QList<float>?

MScottM

Hi all,

In my code I call a function that reads a text file, then uses a RegEx to parse it and then it returns a QStringList of comma separated values that I'm searching for (example): "13:53:33,479, 323.05" - the first is a timestamp, the next is the ID of the value within the timestamp (i.e. at time 13:53:33 there were 479 values recorded) and the last is the specific value I'm looking for. This part is working great (though the regex seems to be slow!).

I want to use the time/value pairs to graph the data in a QCustomPlot and I've been struggling to extract the value out and convert it to a list of floats for the graph. Using an answer from this forum, I have been able to separate the QStringList and create a QList with the three items:

void MainWindow::graphSelected(QStringList _graphingData) {
    graphingData = _graphingData;
    QStringList a{graphingData};
        QList<QStringList> list;
        foreach (const QString &s, a) {
        list.append(s.split(","));
       }
        qDebug() << data;
    }

which gives me this list (qDebug() << data): ("14:09:17", "843", " 396.824"), ("14:09:18", "342", " 396.824")...

For the life of me, I can't seem to figure out how to then iterate through and pull out the third item ("396.824"), convert it from a list of strings to a list of floats.

Any tips?

Thanks and best regards!

Paul Colby

Hi @MScottM,

Converting to a list of floats should be pretty easy, something like:

void graphSelected(const QStringList &_graphingData) {
    QList<QStringList> list;
    QList<float> floats;
    foreach (const QString &s, _graphingData) {
        const QStringList parts = s.split(",");
        list.append(parts);
        Q_ASSERT(parts.size() >= 3);
        floats.append(parts.at(2).toFloat());
    }
    qDebug() << list;
    qDebug() << floats;
}

This gives, for example:

(("14:09:17", "843", " 396.824"), ("14:09:18", "342", " 396.824"))
(396.824, 396.824)

Where the first output line is a list of list of strings, whereas the second line is a list of floats with matching top-level indexes.

Note also, I've added an a Q_ASSERT to say that we expect there will always be at least three items per record. This is fine for dev, but if this is not guaranteed, then drop the Q_ASSERT and do something like this instead:

floats.append(parts.size() < 3 ? NAN : parts.at(2).toFloat());

That will ensure that the two lists still maintain the same indexes when values are missing. Of course, you can detect / handle missing values lots of other ways too.

Also, depending on your case, you might want to define a class or struct to hold the tuple (the three values on each row), and use a QList<MyRowType> instead of both QList<QStringList> and QList<float> together. But that depends on what you want to do once you've parsed the data.

PS I see no need for regex anywhere here... if you explain what you're using it for, then we might be able to help there too.

Cheers.

MScottM

Yes! thanks @Paul-Colby - It works - as usual the code was simple, I just didn't have the experience to figure it out.