How do I exclude data coordinates from a preexisting array?

2015 10 5
1 个回答
回答已采纳
更新时间：2015 10 5
7 次查看（30 天）

0 个投票

Hello!
I was wondering if anyone could help me, I am working on a project where I have a set of data inside of a matrix and I want to create a new matrix with that data using only points outside of an area defined by two functions.
For example, If I use data=rand(100,2) to create a 100X2 matrix and plot it, there is a seemingly random distribution of points. Let's say I plot y1= .5x+.45 and y2=.5x+.55. There will be some many of points inside of these two functions that I DON'T want to include in my data. How would I go about taking these out of the matrix and how would I go about plotting everything but those points?
I tried doing something like this:
>clear all
>close all
>x=linspace(-1,1,100);
>y=linspace(-1,1,100);
>limit1=.5*x+.45;
>limit2=.5*x+.55;
>data=rand(100,2);
>hold on
>plot(x,limit1);
>plot(x,limit2);
>xlim([0,1]);
ylim([0,1]);
>
>if data(:,2) < transpose(limit1)
>scatter(data(:,1),data(:,2),'r','o');
>if data(:,2) > transpose(limit2)
>scatter(data(:,1),data(:,2),'r','o');
>end
>else scatter(data(:,1),data(:,2),'*');
>end
Unfortunately it doesn't seem like it wants to plot the scatter plots correctly and I have no idea how to even start to remove the elements that don't satisfy the conditions from the array, any help would be greatly appreciated!

请先登录，再回答此问题。

 采纳的回答

James Tursa
James Tursa 2015-10-5
编辑：James Tursa 2015-10-5

0 个投票

E.g., use logical indexing to isolate the points you want to plot.
g1 = data(:,2) < .5 * data(:,1) + .45; % Points less that lower limit
g2 = data(:,2) > .5 * data(:,1) + .55; % Points greater than upper limit
g = g1 | g2; % Union of the two point sets above
plot(data(g,1),data(g,2),'*'); % Plot only those points using g as 1st index
If you wanted to physically remove the unwanted points from your data set, then you could do this:
data = data(g,:); % Keep only the wanted points

4 个评论
显示 2更早的评论 隐藏 2更早的评论

Cody Stein
Cody Stein 2015-10-5
Oh my goodness, thank you so much! so if I unsuppress g, will it give me the matrix that has only the points that satisfy those conditions or is it going to give it to me with 1's and 0 stating true or false for each of those 100 rows?
James Tursa
James Tursa 2015-10-5
编辑：James Tursa 2015-10-5
g is a logical vector of 1's and 0's matching the conditions you set forth. ~g is a logical vector of the remaining points, which can also be used for indexing. E.g.,
plot(data(g,1),data(g,2),'*'); % Plot only those points meeting criteria
plot(data(~g,1),data(~g,2),'r*'); % Plot the other points in red
Your data is still your data ... it is not changed to 1's and 0's if that is what you are asking. The logical vector g is only used to select the data ... it doesn't change the values of the data.
Cody Stein
Cody Stein 2015-10-5
So if I wanted the new matrix that included only the data points that satisfied the conditions how would I go about getting that value? Would I multiply each column of data by the logical matrix 'g'? I might be doing that incorrectly because when I do that I get what appears to be a single answer.
James Tursa
James Tursa 2015-10-5
Already answered above. The following line creates a new matrix consisting only of the data points that match your conditions (i.e., keeps all x-y pairs that match the conditions):
data_new = data(g,:); % Keep only the wanted points

请先登录，再进行评论。

更多回答（0 个）

类别

在 帮助中心 和 File Exchange 中查找有关 Scatter Plots 的更多信息

产品

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by