How to separate points under a line in a scatter plot

Question

UH 2022-11-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1840478-how-to-separate-points-under-a-line-in-a-scatter-plot

编辑： Eric Delgado 2022-11-1

采纳的回答： Eric Delgado

x.mat
y.mat

在 MATLAB Online 中打开

I have x-y data set. I want to plot these data and then pick all the coordinates under a specific line.

My code is given below:

clc

clear all

close all

%Importing xy data

Datax= load('x.mat');

x = Datax.x;

Datay= load('y.mat');

y = Datay.y;

%plotting the data

scatter(x,y,".", 'LineWidth',2,MarkerEdgeColor="#1A5276", SizeData=40)

hold on

line ([0 2000], [0 200],'LineStyle','--','color',[0.5, 0.5, 0.5],'linewidth',1)

xlabel('x', 'Color','k');

ylabel('y', 'Color','k');

In the output above, I want to pick the x-y coordinates of the points that lie under the line. For now I am working in a very counterintuitive way by first counting the number of points (4 points in this graph), then I use

g = ginput(4);

After this I click on all those points. Then I use

D = pdist2([x y],g);

[~,ix] = min(D);

to find the indices of those points.

However, I have data set of more than 50,000 points and it is very exhausting. Is there a way to automate this procedure?

Much appreciated. Thanks

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Answer 1

Eric Delgado 2022-11-1

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1840478-how-to-separate-points-under-a-line-in-a-scatter-plot#answer_1088303

编辑：Eric Delgado 2022-11-1

在 MATLAB Online 中打开

Try this...

% Data
xData = Datax.x;
yData = Datay.y;
% Reference line: y = ax + b
% Using your data, a = 200/2000 and b = 0
yLine = .1 * xData;
idx = yLine > yData;
% Plot
figure
scatter(xData(~idx), yData(~idx), ".", 'LineWidth', 2, MarkerEdgeColor="#1A5276", SizeData=40)
hold on
scatter(xData(idx), yData(idx), "ro")
line([0, max(xData)], [0, .1*max(xData)], 'LineStyle', '--', 'color', [0.5, 0.5, 0.5], 'linewidth', 1)
xlabel('x', 'Color','k');
ylabel('y', 'Color','k');
hold off
% Index of the data under reference line
idx = find(idx)