2d arry sorting

i have 2d array which consist of

1. ). 1st row for y axis coordinate of point(i)
2. ). 2nd row for x axis coordinate of point(i)
3. ). ilet consider following

a(1,:)=[1,2,3,4,10,11,12,13,19,20,21,22];

a(2,:)=[4,1,3,2,4,3,1,2,3,2,4,1];

a(3,:)=[1,2,3,4,5,6,7,8,9,10,11,12];

according to the above array 'a' it shows that it is shorted according to the first column(according to y coordinates).

but in my case i want to sort them with following steps

• identify the position where the difference between two consecutive values of y coordinates (values of a(a,:)) changes rapidly and
• sort the values between those rapidly change with respect to x coordination (a(2,:))

let consider the following

a =

     1     2     3     4    10    11    12    13    19    20    21    22
     4     1     3     2     4     3     1     2     3     2     4     1
     1     2     3     4     5     6     7     8     9    10    11    12
     0     1     1     1     6     1     1     1     6     1     1     1

here 4th row represent the difference between two consecutive y coordinates (a(1,:))

in there 5th value shows rapid change so i want consider first 4 value set and analyze the x and y coordinates w.r.t x coordinate (a(2,:))

in same way for whole array and following array represented the expected results.

a =

     2     4     3     1    12    13    11    10    22    20    19    21
     1     2     3     4     1     2     3     4     1     2     3     4
     1     2     3     4     5     6     7     8     9    10    11    12
     0     1     1     1     6     1     1     1     6     1     1     1

note by:

the 3rd column value should not be changed.

the rapid changed is not obtained in same period like in above it varying.(in my case it happened after every 4 values )

the rapid change is not 6 for every instant (let the solution should convenience for values greater than 3)

• can any one help me to code this*

[Sahan Priyanga]

thanks for your quick response, it is worked correctly.

but i'm stuck in following situation. I have think i can manage it but it is really difficult to manage in the case when those are stored in structured cell array.

in my case both x and y coordinates are in 'Centroid' field and many other columns/field also there(s.t. boundingbox,fixelvalue which are related to certain images).

the simply meaning is that when sorting i want to move they also without changing their original position.

Answer 1

[Renato Agurto]

Hi,

is this what you want?

Cheers!

Renato

 clear

 a(1,:)=[1,2,3,4,10,11,12,13,19,20,21,22];
 a(2,:)=[4,1,3,2,4,3,1,2,3,2,4,1];
 a(3,:)=[1,2,3,4,5,6,7,8,9,10,11,12];

 N = size(a,2);

 %Create 4th row
 a(4,1) = 0;
 a(4,2:end) = a(1,2:end) - a(1,1:end-1);

 delta = 3;

 i1 = 1;
 for i = 1:N
    %find range to sort i1:i2
    if i == N || a(4,i+1) > delta
        i2 = i;
        %extract the part of the 2d-array to be sorted
        tmp_a = a(1:2,i1:i2);
        [~, I] = sort(tmp_a(2,:));
        %put it back in the 2d-array
        a(1:2,i1:i2) = tmp_a(1:2, I);
        i1 = i+1;
    end
 end

Answer 2

[Guillaume]

Here's how I'd do it:

a = [1     2     3     4    10    11    12    13    19    20    21    22
     4     1     3     2     4     3     1     2     3     2     4     1
     1     2     3     4     5     6     7     8     9    10    11    12];
splitlength = diff([0 find(diff(a(1, :)) >= 3) size(a,2)]); %find distance between rapid changes
splita = mat2cell(a([1 2], :), 2, splitlength);  %split 1st two rows of into sub matrices
sortedsplita = cellfun(@(m) sortrows(m', 2)', splita, 'UniformOutput', false); %sort submatrices by second row
sorteda = [cell2mat(sortedsplita); a(3, :)] %recombine submatrices and 3rd row of a

Vectorised code, so should be fast.