How to carry index within a function?

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Xiaohan Du 2016-11-16

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评论： Xiaohan Du 2016-11-16

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Hi all,

This is a very long question ;-)

I have a function which sort a grid to cell blocks, the function is:

function [otpt] = GridtoBlock(inpt)
xy = cellfun(@unique, num2cell(inpt, 1), 'UniformOutput', false);
x = xy{1};
y = xy{2};
otpt = cell(numel(y) - 1, numel(x) - 1);
for xidx = 1 : numel(x) - 1
   for yidx = 1 : numel(y) - 1
      otpt{yidx, xidx} = [repmat(x(xidx:xidx+1), 2, 1), repelem(y(yidx:yidx+1), 2)];
   end
end
for i_rte = 1:numel(otpt)
    otpt_temp = otpt{i_rte};
    otpt{i_rte}(3, :) = otpt_temp(4, :);
    otpt{i_rte}(4, :) = otpt_temp(3, :);
end

If the inpt is (a square domain contains 3 by 3 points):

inpt_noindex = [-1 -1; -1 1; 1 -1; 1 1; -1 0; 0 -1; 0 0; 0 1; 1 0];

then the otpt is:

otpt_noindex = 
      [4x2 double]    [4x2 double]
      [4x2 double]    [4x2 double]
otpt_noindex{:}
ans =
      -1    -1
       0    -1
       0     0
      -1     0
ans =
      -1     0
       0     0
       0     1
      -1     1
ans =
       0    -1
       1    -1
       1     0
       0     0
ans =
       0     0
       1     0
       1     1
       0     1

i.e. the function automatically sort the x and y coordinates and put them into a 2 by 2 cell block.

Now my question is, if I find the row index of inpt, i.e.

inpt_index = [1 -1 -1; 2 -1 1; 3 1 -1; 4 1 1; 5 -1 0; 6 0 -1; 7 0 0; 8 0 1; 9 1 0];

How can I modify the function to get the otpt with the original row index? i.e. I want the otpt to be

otpt_index = 
      [4x3 double]
      [4x3 double]
      [4x3 double]
      [4x3 double]
otpt_index{:}
ans =
       1    -1    -1
       6     0    -1
       7     0     0
       5    -1     0
ans =
       5    -1     0
       7     0     0
       8     0     1
       2    -1     1
ans =
       6     0    -1
       3     1    -1
       9     1     0
       7     0     0
ans =
       7     0     0
       9     1     0
       4     1     1
       8     0     1

The goal is to make the row index follows the matrix operation. I have written a for loop using isequal to compare each block against the inpt, but this is not efficient when the inpt becomes large.

Thanks a lot!

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KSSV 2016-11-16

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for

inpt = [1 -1 -1; 2 -1 1; 3 1 -1; 4 1 1; 5 -1 0; 6 0 -1; 7 0 0; 8 0 1; 9 1 0];

your otpt is of size 2X8 with element as 4x2 double. This you want to change to what size?

Xiaohan Du 2016-11-16

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Hi KSSV,

For

inpt_index = [1 -1 -1; 2 -1 1; 3 1 -1; 4 1 1; 5 -1 0; 6 0 -1; 7 0 0; 8 0 1; 9 1 0];

I'd like to have the same sort method, but only 'carry' the original index with the sorted blocks.

If you compare the otpt_index against otpt_noindex, you'll find that otpt_index is the 2nd and 3rd column of otpt_noindex, the only difference between otpt_index and otpt_noindex is the 1st column of otpt_index, which is the original row index from inpt_index.

I hope this is clear.

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