How do I make different groups within a matrix?
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I have a 2904x3 matrix where each column represents the x, y and z coordinates of some vectors. Some of these vectors have the same z-coordinate and I need to group those together. Any ideas?
3 个评论
Mathieu NOE
2021-3-12
hello
have you tried with unique ?
a = [1 1 1 2 2 2 3 3 4 4];
[C,IA,IC] = unique(a);
C =
1 2 3 4
IA =
1
4
7
9
IC =
1
1
1
2
2
2
3
3
4
4
Jaime Castiblanques
2021-3-12
Adam Danz
2021-3-12
Extending Mathieu NOE's suggestion, the 3rd output to unique is a grouping variable but you should use the stable flag to ensure that the grouping values correspond to each element of the vector.
% xyz is nx3 matrix of [x,y,z] values
[~,~,zgroup] = unique(xyz(:,3));
Alternatively, if you just want to sort the matrix according to the z column,
xyzSort = sortrows(xyz,3);
采纳的回答
Veronica Taurino
2021-3-12
编辑：Veronica Taurino
2021-3-12
How do you need to get arrays associated?
Try this:
clear all
close all
x= (50)*rand(50,1);
y= (50)*rand(50,1);
z= (50)*rand(50,1);
% I create 4 equal z coordinates:
z(12)=z(23);
z(34)=z(23);
z(1)=z(23);
z(45)=z(23);
z(23)
% Put all together
AA= [x,y,z];
% Look for index
[~, ind] = unique(AA(:, 3), 'rows');
% DUPLICATE INDEX
duplicate_index = setdiff(1:size(AA, 1), ind) % This finds the indexes of duplicates
% duplicate values
duplicate_value = AA(duplicate_index, :) % This extracts the arrays with duplicates
results:
z(23) =
12.6859 % the Z value I imposed
duplicate_index = % indexes of duplicates the script finds
12 23 34 45
duplicate_value = % array with same Z the script finds
19.6717 40.5660 12.6859
47.5017 3.6415 12.6859
11.9746 35.4336 12.6859
38.4967 19.0424 12.6859
6 个评论
Veronica Taurino
2021-3-12
Note that in reality you may have values of z coordinates very close, that you can consider the same but due to the double data type used you will not be able to group the two as identical using (say) unique, For example
1.1234567
1.1234568
Jaime Castiblanques
2021-3-12
Veronica Taurino
2021-3-12
编辑：Veronica Taurino
2021-3-12
It is just a way to set equal z's coordinates over the arrays I randomly created.
If you need to group points with equal Z's, you can change the previous code as follows:
x= (50)*rand(50,1);
y= (50)*rand(50,1);
z= (50)*rand(50,1);
% I create 2 GROUPS of equal z coordinates:
% First group
z(12)=z(23);
z(34)=z(23);
z(1)=z(23);
z(45)=z(23);
z(23);
% Second group
z(1)=z(50);
z(28)=z(50);
z(11)=z(50);
z(50);
% Put all together
AA = [x,y,z]; %%%%% YOU WOULD START FROM HERE WITH YOUR DATA %%%%%%%%%
% Sort
AA_sorted=sortrows(AA,3);
% Look for index
[C,ia,ic] = unique(AA_sorted(:, 3), 'rows');
% DUPLICATE INDEX
duplicate_index2 = setdiff(1:size(AA_sorted, 1), ia);
% duplicate values
duplicate_value2 = AA_sorted(duplicate_index2, :);
% Look for index GROUP
[C3,ia3,ic3] = unique(duplicate_value2(:, 3), 'rows');
% Create group
for jj=1:length(ia3)
if jj<length(ia3)
Group{jj}=duplicate_value2(ia3(jj):ia3(jj+1)-1,:);
else
Group{jj}=duplicate_value2(ia3(jj):end,:);
end
end
In this way, I get the different groups grouped in a cell array. Be aware of my previous note and link.
Jaime Castiblanques
2021-3-14
Veronica Taurino
2021-3-15
I think it may happen what I told you in the comment above, with dedicated link. Did you check it?
Jaime Castiblanques
2021-3-15
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