Labels for each point in ScatterPlot #2141

Cubikon · 2022-09-30T09:44:19Z

Cubikon
Sep 30, 2022

I have data with x/y values and a text value for each point. I use a Scatterplot and each point has the text added as a AddText() at the X/Y coordinates with the value as lable. This is ok, but annoying, if i want to change one value.
I would like the posibility to give addScatterPlot() a 3rd array to set a label for each point. And the posibility to use the Update() method to change them.

Example:

double[] xs = { 1, 2, 3, 4, 5 };
double[] ys = { 1, 4, 9, 16, 25 };
string[] labels = {"label1","label2","label3" ,"label4","label5"};
var plt = new ScottPlot.Plot(400, 300);
var scatter =plt.AddScatter(xs, ys, labels, color: Color.Red, lineWidth: 2);

string[] labels2 = {"change1","change2","change3" ,"change4","change5"};
scatter.UpdateZ(labels2);

swharden · 2022-10-06T02:13:51Z

swharden
Oct 6, 2022
Maintainer

Hi @Cubikon,

I agree that's a bit clunky, but it's the best available way I'm aware of using existing code.

Adding an array of string labels to scatter plots would be possible though! If the array is empty or null, it would skip over it, but if populated it could render each label. If you're interested in creating a PR to add that feature, it could be inserted in the following region, and I'd be happy to review it! (#2010)

I probably won't do this myself, but I'll add information here in case you (or someone else) wants to add this functionality and create a pull request 👍 🚀

Storing Labels

Rather than adding a UpdateZ() function, I'd just add a field users can optionally assign to, something like this:

public string[] DataPointLabels = null;

somewhere around here:

ScottPlot/src/ScottPlot4/ScottPlot/Plottable/ScatterPlot.cs

Lines 16 to 19 in 4008bdf

    
           public double[] Xs { get; private set; } 
        
           public double[] Ys { get; private set; } 
        
           public double[] XError { get; set; } 
        
           public double[] YError { get; set; }

Rendering Labels

Then in the render function just below this section

ScottPlot/src/ScottPlot4/ScottPlot/Plottable/ScatterPlot.cs

Lines 425 to 429 in 4008bdf

    
           // draw a marker at each point 
        
           if ((MarkerSize > 0) && (MarkerShape != MarkerShape.none)) 
        
           { 
        
               MarkerTools.DrawMarkers(gfx, points, MarkerShape, MarkerSize, MarkerColor, MarkerLineWidth); 
        
           }

You could add some logic to check if the array contains items, and if so iterate points and render the text. You can copy text rendering logic from the marker plot class

ScottPlot/src/ScottPlot4/ScottPlot/Plottable/MarkerPlot.cs

Lines 94 to 105 in 4008bdf

    
           SizeF stringSize = Drawing.GDI.MeasureString(gfx, Text, TextFont.Name, TextFont.Size, TextFont.Bold); 
        
           gfx.TranslateTransform(point.X, point.Y); 
        
           gfx.RotateTransform(TextFont.Rotation); 
        
           (float dX, float dY) = Drawing.GDI.TranslateString(gfx, Text, TextFont); 
        
           gfx.TranslateTransform(-dX, -dY); 
        
           using var font = Drawing.GDI.Font(TextFont); 
        
           using var fontBrush = new SolidBrush(TextFont.Color); 
        
           gfx.DrawString(Text, font, fontBrush, new PointF(0, 0)); 
        
           Drawing.GDI.ResetTransformPreservingScale(gfx, dims);

That code is a little fancy because it lets you customize alignment, but it should get you started!

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Labels for each point in ScatterPlot #2141

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Cubikon Sep 30, 2022

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swharden Oct 6, 2022 Maintainer

Storing Labels

Rendering Labels

Cubikon
Sep 30, 2022

swharden
Oct 6, 2022
Maintainer