如何对MATLAB中的绘制点进行分类？

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Ángel González 2018年8月23日

Edited: 数学工作Support Team on 3 Sep 2020

接受的答案： Ángel González

你好！我有一个关于绘图点的问题。在我的项目中，我得到了 X and y coordinates and plotting them just when I read them from the socket, and I get something like this:

Just after plotting the coordinates I'm indexing them in two different vectors (one for Xcoordinates and the other for ycoordinates )。问题是,当我try to plot them again in another script (or in another figure) the result is not what I expected.

The code I use for plotting the points the second time is:

                         数字（）
                        
                         为了i = 1：1000％1000是x_vector和y__vector的长度
                        
                         绘图（x_vector（i），y_vector（i），'o'）
                        
                         抓住on
                        
                         轴（[0 1920 0 1080]）;
                        
                         set(gca,'ydir'，，，，'撤销'，，，，'xaxislocation'，，，，'最佳'）
                        
                         结尾

这是先前代码的结果：

I guess that the second time I try to plot the two vectors 阴谋正在尝试通过一些回归打印一些线性函数，而不是打印我期望的点云。

Thank you

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dpb 2018年8月23日

Simply store the points as you receive them...you don't show code but

                               % preallocate
                              
                               n = npts;
                              
                               X_vector=zeros(npts,1);
                              
                               y_vector = x_vector;
                              
                               % collect, save...
                              
                               为了i = 1：npts
                              
                               % return x, y, here...
                              
                               x_vector（i）= x;
                              
                               y_vector(i)=y;
                              
                               % do whatever else with x,y during download
                              
                               ...
                              
                               结尾

假设您先验您要收集多少点。如果未知，请从数量大开始，然后删除不需要的那些。

另外，尽管以这种方式进行编码不是有效的，但是您上面写的正如您所写的动态分配是简单但高架的 -

                               X_vector=[]; y_vector=[];
                              
                               whilestilldownloading()
                              
                               % get x, y
                              
                               x_vector = [x_vector; x];
                              
                               y_vector = [y_vector; y];
                              
                               ...
                              
                               结尾

will keep each x,y pair together.

dpb 2018年8月23日

That's calling sort repetitively every iteration...there's no indication of needing them sorted; if do, far more efficient to wait until done collecting and then sort the whole vector once.

当然，根据排序X的顺序保持和重新排序Y是必须保持两者之间的关联。

或者，一个人可以做 slightly differently as

                               Xy=[];
                              
                               whilecollecting()
                              
                               % get x, y
                              
                               Xy=[xy; [x y]];
                              
                               ...
                              
                               结尾
                              
                               Xy=sortrows(xy);