Delete Array Element Based on Conditions

Hello,

I have an array Coordinates 3133x3 that contains the 3 coordinates (x,y,z) of a list of points. Column 1 is the x, column 2 the y and column 3 the z.

Inside this array I would like to remove some points (rows) besed on 2 different conditions:

1) Delete all points (so delete the corresponding rows in Coordinates) with z-coordinates that is more than +-5 aways from this reference z_ref array.

So for example if a point has z-coordinate 400 it will be deleted, contrary if it has z-ccordinate 410 or 412 it will be keeped. This to remove the outliers present.

z_ref = [411.2966 426.2966 441.2966 456.2966 471.2966 486.2966 501.2966 545 575 605 635 665 695];

2) If there are more points with the same z-coordinate (again in a range of +-5) keep just the one with the z-coordinate closer to z_ref. This the remove coinciding points and keeping just one.

for i = 1:length(Coordinates)
    for j = z_ref
        if Coordinates(i,3) >= j + 5 || Coordinates(i,3) <= j - 5
            Coordinates(i,:) = [];
        elseif Coordinates(i,3) <= Coordinates(i+1,3) + 5 || Coordinates(i,3) >= Coordinates(i+1,3) - 5
            Coordinates(i+1,:) = [];
        end
    end
end

This is what I tried but it doesn't work.. Otherwise I was checking other methods like mask but still I was not able to make it works

Please help me, thanks in advance

Answer 1

[Chunru]

load Coordinates.mat
z_ref = [411.2966 426.2966 441.2966 456.2966 471.2966 486.2966 501.2966 545 575 605 635 665 695];
for i = 1:length(Coordinates)
    if min(abs(Coordinates(i,3) - z_ref)) >= 5
        Coordinates(i,3) = nan;
    end
end
Coordinates(isnan(Coordinates(:,3)), :) =[];

for i=1:length(z_ref)
    within5 = find(abs(Coordinates(:, 3) - z_ref(i))<5);
    [~, idx] = sort(abs(Coordinates(within5, 3) - z_ref(i)));
    if length(idx)>1
        Coordinates(within5(idx(2:end)), :) =[];
    end
end

Coordinates

Coordinates = 11×3

95.0460 -7.8772 543.5237 34.2147 -8.4905 426.8342 64.3050 -3.5719 441.3390 34.6908 -9.2050 457.0454 96.6137 -28.8350 631.4779 95.4812 -14.4214 573.1167 96.0615 -21.6073 602.2293 96.7264 -35.9699 660.8084 93.3768 3.1698 471.1664 93.9380 2.5895 501.2340

[Fabio Taccaliti]

Thanks Chunru for the answer! This is exactly what I was looking for :)

What is the function of the min in the if condition?

This script that you wrote here is doing just the first condition that I put in the question right? Delete points +-5 aways from the reference.

How can I implement also the second condition that removes all the points too close to each other?

[Chunru]

For the second part, you may want to post some sample data.

[Fabio Taccaliti]

Thanks for the reply, I attached the Coordinates array after the first iteration, with the code that you suggested.

load Coordinates.mat

Please let me know :)

[Chunru]

See above

[Fabio Taccaliti]

Thanks a lot for it!! :)