regroup identical coordinate pair

Hi everyone,

I've got vectors like this corresponding to the coordinates of a point:

X = [1;1;8;5;5;6]

Y = [2;2;5;6;6;7]

and would like to regroup points that have the same coordinates and have the following results :

R_X = [1;8;5;6];

R_Y = [2;5;6;7];

Are there any functions or way to concatenate that would help me to do that ?

Thanks

Answer 1

[Star Strider]

I have no idea what your objective is, however the unique function will produce the result you posted:

RX = unique(X,'stable')
RY = unique(Y,'stable')

producing:

RX =

     1
     8
     5
     6


RY =

     2
     5
     6
     7

[kix]

Thank you for you answer,

I have a matrix composed of X and Y: M=[X,Y]

And I would have the following result:

Res = [1,2;8,5;5,6;6,7]

And I would like also to found the indexes where the duplicates values were found for exemple :

For X=1 and Y=2 (row 1) I would have the indexes 1 and 2

For X=8 and Y=5 (row 2) I would have index 3 etc

The function unique gives me indexes

I have tried the function unique but it only gives me one index for the values

[Star Strider]

My pleasure!

This works:

M = [X Y];
[Res,~,ic] = unique(M, 'rows', 'stable')
ix = accumarray(ic, (1:size(M,1)).', [], @(x){x})

for k = 1:size(Res,1)
    Out = [Res(k,:) [ix{k}].']                      % Output Loop (Display Only º Discard)
end

producing:

Res =
     1     2
     8     5
     5     6
     6     7

and:

Out =
     1     2     1     2

Out =
     8     5     3

Out =
     5     6     4     5

Out =
     6     7     6

This also demonstrastes how to access the processed data.

.

[kix]

Thank you, this worked perfectly,

A last question if it doesn’t bother you,

Each point that I have got different characteristics such as temperature and humidity for example (they are different for every point even if they have the same coordinates in X and Y).

Temp = [22;26;23;20;25;27]

Now that I got indexes, of the points that have the same coordinates I would like to build an array containing the corresponding temperature of these point like this :

{[22,26];[23];[20,25];[27]}

I’ve tried with a for loop but it doen’t fill the cell correctly

Thank you in advance

[Star Strider]

My pleasure!

That’s a minor variation on my previous code:

Temp = [22;26;23;20;25;27];
M = [X Y Temp];
[Res,~,ic] = unique(M(:,[1 2]), 'rows', 'stable')
ix = accumarray(ic, (1:size(M,1)).', [], @(x){M(x,3)})

for k = 1:size(Res,1)
    Out = [Res(k,:) [ix{k}].']                      % Output Loop (Display Only º Discard)
end

producing:

Out =
     1     2    22    26

Out =
     8     5    23

Out =
     5     6    20    25

Out =
     6     7    27

That appears to do what you requested.

EDIT — (7 Jun 2020 at 14:59)

To save all the results to a matrix:

MaxCols = max(cellfun(@numel,ix));                  % Maximum Number Of Temperatures For Any Location
Out = NaN(size(Res,1),2+MaxCols);                   % Preallocate: ‘NaN’ Matrix
for k = 1:size(Res,1)
    Out(k,1:(2+numel(ix{k}))) = [Res(k,:) [ix{k}].'];
end
Out                                                 % Display Results (Optional)

producing (for this example):

Out =
     1     2    22    26
     8     5    23   NaN
     5     6    20    25
     6     7    27   NaN

.

[kix]

Thank you for you help !

[Star Strider]

As always, my pleasure!

Answer 2

[Adam Danz]

[~, unqIdx] = unique([X(:), Y(:)], 'rows','stable');
R_X = X(unqIdx); 
R_Y = Y(unqIdx);