Set points that matches with a vector as NaN

load('var.mat')
scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on
scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');
scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

whos cy

  Name          Size              Bytes  Class     Attributes

  cy        46057x4             1473824  double              

cy is a 4 columns matrix, I would like to set all the values of cy(:,4) that matches with the positiones above top vector and below bot vector as NaN values.

Answer 1

[Dave B]

In this particular case, because they all have the same y value, you can do this quite easily with interp:

scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on
scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');
scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

ind = cy(:,4) < interp1(bot(:,1),bot(:,3),cy(:,1)) | ...
            cy(:,4) > interp1(top(:,1),top(:,3),cy(:,1));
cy(ind,4) = nan;
scatter3(cy(:,1),cy(:,2),cy(:,4),10,'m','filled');hold on

[Philippe Corner]

Hi Dave,

I did not undertand your approach.. it did not work actually.

There are some points in cy(:,3) matrix with values in cy(:,4). These points are located in [cy(:,1) cy(:,2) cy(:,3)] above and below [top(:,1) top(:,2) top(:,3)] and [bot(:,1) bot(:,2) bot(:,3)] , im trying to change the cy(:,4) values that matches these conditions to NaN.

[Dave B]

The way that i understood your problem was that you have top which contains x,y,z co-ordinates for a top, and bot which contains x,y,z co-ordinates for a bottom.

Looking at your data, it was clear that the y values were irrelevant: all of the values are the same plane.

So I used interp1 to find the relvant z value for each x value. The expression:

interp1(bot(:,1),bot(:,3),cy(:,1))

says to find the z co-ordinate of the bottom by interpolating, using the x cordinate in cy and the mapping of x to z established in bot.

Below I've attached the result (I had to re-include the file): you can see that the values of cy(:,4) which are above and below top and bot have been removed.

load('var.mat')
scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on
scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');
scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

ind = cy(:,4) < interp1(bot(:,1),bot(:,3),cy(:,1)) | ...
            cy(:,4) > interp1(top(:,1),top(:,3),cy(:,1));
cy(ind,4)=nan;
scatter3(cy(:,1),cy(:,2),cy(:,4),10,'m','filled');hold on

[Philippe Corner]

Thanks a lot for your kind dispositon Dave,

Maybe I did not express myself properly. So, if we plot the cy matrix like this:

load('var.mat')
scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on
scatter3(cy(:,1),cy(:,2),cy(:,3),10,cy(:,4),'filled');% with the cy(:,4) values that we want to set NaN
scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');
scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

you can see that above the top and below the bottom, there are some cy(:,4) values. I want to use indexes to find the positions and change them to NaN so all the plot:

scatter3(cy(:,1),cy(:,2),cy(:,3),10,cy(:,4),'filled');% with the cy(:,4) values that we want to set NaN

set the cy values only inside top and bot boundaries.

Thanks a lot!

[Dave B]

@Philippe Corner - Sorry that was totally my fault. I was incorrectly thinking about the matrix in the cy matrix.

I was checking cy(:,4) against bot(:,2)/top(:,3) but I think the answer is basically the same but I should have been checking against cy(:,3) - which in hindsight makes a lot of sense! Is this the correct cropping?

load('var.mat')
scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on

scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');
scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

ind = cy(:,3) < interp1(bot(:,1),bot(:,3),cy(:,1)) | ...
            cy(:,3) > interp1(top(:,1),top(:,3),cy(:,1) ,'nearest');

cy(ind,4)=nan;
scatter3(cy(:,1),cy(:,2),cy(:,3),10,cy(:,4),'filled');hold on

[Philippe Corner]

Thank you very much for your help. And this approah using interp1 is very interesting idea to solve this task.

Best wishes!

[Philippe Corner]

Hi Dave, this quiestion is very similar tham this one, but im confused about how to use it for all X, Y, Z positons. If you can give a hand it would be highly appreciated! https://it.mathworks.com/matlabcentral/answers/1413272-how-to-change-the-c-values-that-matches-a-3-coordinates-position-condition