Finding maximum y value for the same x values and corresponding z values

x y
1 5
1 7
1 9
2 8
2 22
2 11
5 5
5 10
5 20

I'd like to spit out an array of the max y coordinate that corresponds to each x coordinate. So I am using the following code provided in the community:

[uv,~,idx]  = unique(xy(:,1)); %what do they correspond to?
xmax = accumarray(idx,xy(:,2),[],@max); %build matrix
[uv xmax]

My question is that if I have additional z column

z
1
9
7
8
6
5
3
2
4

then how can I also pick up the corresponding z values?

Answer 1

[Star Strider]

Use the ismember function with the 'rows' option:

xy = [1 5
1 7
1 9
2 8
2 22
2 11
5 5
5 10
5 20];

z = [1
9
7
8
6
5
3
2
4];

xyz = [xy z];

[uv,~,idx]  = unique(xy(:,1)); %what do they correspond to?
xmax = accumarray(idx,xy(:,2),[],@max); %build matrix
Result = [uv xmax];

[~, ix] = ismember(Result(:,1:2), xyz(:,1:2), 'rows');

All_Columns = xyz(ix,:)

All_Columns =

       1     9     7
       2    22     6
       5    20     4

Answer 2

[Andrei Bobrov]

T = table(x,y,z,'Va',{'x','y','z'});
out = varfun(@max,T,'gr','x');

or

z=[...
1
9
7
8
6
5
3
2
4];
xy = num2cell(...
[1 5
1 7
1 9
2 8
2 22
2 11
5 5
5 10
5 20],1);
[x,y] = xy{:};

xyz = [x,y,z];
[~,~,jj] = unique(x);
idx = accumarray(jj,(1:numel(x))',[],@(ii)ii(max(y(ii)) == y(ii)));
out = xyz(idx,:)