Create a matrix from a .csv file

AliM93

Hi everybody, i'm pretty new to Qt. I've a .csv file with 3 columns : xcoord, ycoord and the value in that position, i try to import it into my qt gui (using a tableView) and now i would like to create a matrix and to show it in the graphicsview. (it is a binary matrix in which i have to activate only the elements of the matrix equal to 1.) i'm searching a way to do this, but i haven't found yet. Does anyone have an idea? I'll be very glad to everybody which helps!

mrjj

Hi
So we have a list of x,y,value and you want to draw it as a 2d grid where
all non zero values should be shown ?

Im not really sure how/what you want to draw :)

You could have each x,y be an Item or you could subclass an item and draw it using painter.
It depends on what we want to do with it.
If you want to click on "cells" (x,y) then free items is more fun.

AliM93

Yes! but first i have to store it in a matrix or in a 3d array, because now i visualize those data from a csv file into a qtableview but i can't find out how to save into an array. Yes i want to click on cells and save that coordinates. what i have to develop it is sort of map where user can select points (only the available one (equal to 1) and then the code output the coordinates. so free items is better? thank you a lot!

mrjj

@AliM93
Hi
Im not 100% sure what a 3d array would be so maybe i dont understand it fully what data you have.

I imagine something like

struct DataRow {
float x;
float y;
int value;
}

std::vector<DataRow> Data;

so just a list of x,y,value.

We then plot this list to the matching x,y values but we dont store it as a matrix as such.

But else explain what type of array/3d/matrix you want ?

You can also do
int matrix[maxx][maxy];
So the storage structure is like we want to display it.
This only works well if the limits of x and y is somewhat reasonable.
If they have huge gaps etc then such 1:1 mapping can be annoying.

https://www.tutorialspoint.com/cplusplus/cpp_multi_dimensional_arrays.htm

Yes if you need to be able to select one or more "cells"/points then free item is more fun as we get selection for free. With painter we must add code to be able to know which "cells" that is selected etc. We get that for free with standalone items.

How many points are there ?

AliM93

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mrjj

@AliM93
Ok, it really is super straight. The x,y are perfect for

bool cvsData[14][21];

You say you want to do it in graphicsview.
Do you already use this for the app and need zoom and panning and such ? ( or know it well)

With only 300 points, QPainter is more than fast enough and the coordinate system
matches the x,y values perfectly.

But do you need to let the user select ONLY some of the 1 points ?
We draw all 1 value points to this grid.
User then has to select some of them or what type of interaction is needed ?

Im asking to verify that graphicsview is good to approach versus just to make custom QWidget Grid Draw class.

AliM93

No i don''t already use graphicsview.
Yes, i need to let the user select 3 of 1 points, and i need to save the coordinates of the points selected. I think to create a grid of gray points and to color (for example in green) the 1 points. And yes, the user has to select it clicking on them using the mouse.

mrjj

@AliM93

Ok 100 % clear now.

Well graphicsview/scene are powerfull and awesome but also comes with a quite steep learning curve as
it has multiple coordinate system and many details.
On the other hand, it does provide item selection out of the box. ( and much more)
But you would have to do some reading before being able to create a grid.
A good starting point could be
https://doc.qt.io/qt-5/qtwidgets-graphicsview-diagramscene-example.html
More work but it could handle tons of points and support xoom etc.

In contrast, a custom widget would have to keep track of selection but actually drawing the grid is just a few
lines. Since the x,y are so uniform, calculating the point from mouse pos is quite easy.
Also we just need to override paint event and mouse press and we are there.
I could write you a rough version in 5 mins. ( provided this is NOT homework :)
Such widget would not be able to zoom or pan but simply draw a grid that one can click on.

So Its up to you.
graphics view is the powerful version but might take some time to dig into.
A custom Widget using Qpainter and a few functions to select and deselect.
Since its just 300 points we don't need anything fancy and just redraw the whole gid when something changes.

AliM93

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AliM93

I think i choose Qpainter. It's not a homework, i would like to do it on my own, but i don't even know how to save data in the bool csvData.
https://www.tutorialspoint.com/cplusplus/cpp_multi_dimensional_arrays.htm
i find here some explanation? can you give some hints? thanks

mrjj

@AliM93
For this use case, i would also lean towards a custom widget as its quite simply requirements for the grid.
If you had need zoom or panning, graphicsview.

Good. Just ask if you run into issues.
Creator has wizard to make q custom widget quite fast.
Then you just add PaintEvent and MousePress functions.

In paint event, you want to use the width/height() to get avialable area.
That you use to find out the size of each point./cell/grid size.
so that width()/14
and Height()/21
and you then draw each cell or point or what you want.
You store the size of one cell as a member to use when we click.

Then in mouse Press.
When activated we use event->pos() to know where we click with mouse.
We then use the CellSize we calculated in the paint to find out which cell it must be.
and then paint it.

To keep track of this and have the data i would use:

struct DataPoint {
int x;
int y;
bool value;
QColor DrawColor; // we change this from selected / not selected.
bool isSelected: // we set this when we click on it.
}

and have that struct in

DataPoint Data[14][21];

So we have both data and the color and selection status in one place.

then we can use it like
Data[10][10].iSSelected = true; etc
Data[10][10].DrawColor = Qt:red;

but i don't even know how to save data in the bool csvData.
Well when you read teh file, you get the x,y , right ?
So you just use them to put value in right place.

AliM93

Yes, i can't understand how to save into the bool csvData the right value. when i read the file i get i table view with 3 columns but i don't know how to read them in a proper manner.

mrjj

@AliM93 said in Create a matrix from a .csv file:

Sorry, but when you speak about qcustom widget, you mean that I have to create something from my .ui file? What i should add to show my grid to my .ui file?

Actually its a complete new Widget that we then put on your main UI form.
So the new Widget will contain the painting and the data and be standalone from MainWindow.
Since we do custom painting in the widget, we dont need to give it a UI file as we dont need it here.
Creator can make most of the code for you. Using the new Wizard.
Or you can just type it by hand. Its just to subclass QWidget and the virtual functions.

Yes, i can't understand how to save into the bool csvData the right value. when i read the file i get i table view with 3 columns but i don't know how to read them in a proper manner.

But it sounds like you do spit each line to x,y, value before adding them, to the model you use for the TableView ?

Can you show the code ?

btw: just so you dont think a custom widget is huge work.
its base is like

#ifndef GRIDWIDGET_H
#define GRIDWIDGET_H

#include <QWidget>

class GridWidget : public QWidget
{
    Q_OBJECT
public:
    explicit GridWidget(QWidget *parent = nullptr) : QWidget(parent) {}
protected:
    virtual void paintEvent(QPaintEvent *event) override
    {
    }
    
    virtual void mousePressEvent(QMouseEvent *event) override
    {
    }
};

#endif // GRIDWIDGET_H

AliM93

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mrjj

@AliM93

Ah, yes you do split it. so right there you could stuff into the other list too.
(line 44 first image) line is a StringList and index 0 is x, 1 is y and 2 is value , i assume.

Actually a custom widget is perfect for use in other project as its just its .cpp and h file and if you include it, you can use it.

Btw is the TableView and the GridWidget related ?
it would be possible to reuse the model with your widget if you want to share the data between them but
its more complicated.

AliM93

No the tableview was just a check for me, but i don't have to use it. i just want to show the data in a grid and that's all.
i declare it as a QString, is the same of e StringList? yes the order it's like that anyway

So i have to add a file.h and file.cpp or i can work on this?

mrjj

@AliM93 said in Create a matrix from a .csv file:

No the tableview was just a check for me, but i don't have to use it. i just want to show the data in a grid and that's all.
i declare it as a QString, is the same of e StringList? yes the order it's like that anyway

Ok, just asking as using a model allows to share data views which is super nice if one needs to be able to edit it and have it reflected at once in some other view. But if you just use it to show data and dont want to edit it. then i would just use
some small structure to all data needed for the grid display.

So i have to add a file.h and file.cpp or i can work on this?

You mean if you can use Matrix class for this custom widget ?
Yes, but its a QDialog so not perfect fit. ( unless you always want the Grid to popup over the main window)

AliM93

@mrjj from the main_window a open all the other window. and the matrix is a part of another QDialog. now i splith things in order to understand what i have to do but then i have to embed this as a part o QDaialog window. maybe afert a pushbutton clicked i open my grid, the user select and then push another button and i return to my previous GUI with point selected saved.

So what i have to do now is to add a customgrid.h customgrid.cpp, but what i have to select? to add? if it is not a dialog? a cpp headers and cpp source file separately? or a cpp class?

mrjj

@AliM93
Hi
Well if you want to pop it up anyway, you could leave it as QDialog and draw directly to it but
could be more handy if it was standalone and you would add it to a QDialog but this is not critical.

well you just inherit QWidget instead of QDialog and change in cpp where it calls base in constructor.
xxx) : QDialog(parent) {} -> ) : QWidget(parent) {}

class GridWidget : public QWidget

AliM93

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