plot by skipping some points

Hi all,

I want to plot by skipping some points (4,31), (8, 71) and so on in my data . Is there any straight forward way of doing it?

Thank you

x=[1:1:20];
y=[1:10:200];

%x=c(:,1)

plot (x,y,'o');
 %ismembertol(

[Adam Danz]

It's unclear whether (4,41) and (8,81) in your example are indices or coordinates.

Neither of your vectors have 81 elements so they can't be indicies and the max value in "A" is 20 so that wouldn't work with coordinates as large as 40. So the example doesn't help either.

[Babu Sankhi]

I am sorry about that I just want to plot by skipping some coordinates.

Answer 1

[Adam Danz]

Several methods to plot a subset of values within an array.

1. Indexing. If you want to eliminate a list of (x,y) values, use functions like ismember, ismembertol, or == to create an index of matches, idx. Then use ~idx to select all other values when plotting plot(x(~idx), y(~idx)).
2. Nan-replacement. After finding the values you want to ignore using indexing, replace those values with NaN. x(idx)=NaN; y(idx)=NaN; plot(x,y)
3. Remove unwanted values. After finding the values you want to ignore using indexing, remove them using x(idx)=[]; y(idx)=[]; plot(x,y)
4. To plot every n'th value: plot(x(1:n:end), y(1:n:end));
5. To remove every n'th value: x(1:n:end)=[]; y(1:n:end)=[]; plot(x,y)
6. To plot the n'th, m'th, and p'th values: idx=[n,m,p]; plot(x(idx),y(idx));
7. To eliminate the n'th, m'th, and p'th values: idx=[n,m,p]; x(idx)=[]; y(idx)=[]; plot(x,y)

If you need additional help implementing any of those ideas, show us what you've tried where you're stuck.

[Babu Sankhi]

But ismember just gives the logical array which reapeats , I wonder how does it works in my case there is no repetition of y coordiantes on x!! so confused

[Adam Danz]

> But ismember just gives the logical array which reapeats

Yes, that logical array can be used to select which values are plotted as shown in the first point in my answer. I don't know what you mean by "which repeats"

> in my case there is no repetition of y coordiantes on x!! so confused

I don't know what this means and it's still not clear to me how you'd like to select which values are plotted.

> I just want to plot by skipping some coordinate

Which coordinates? That's still to vague to suggest something specific. I've added methods 4,5,6,7 to my answer in case that's what you're looking for.

[Babu Sankhi]

Thanks for your elaborative ideas.