Need algorithm to create the list

Question

Fayyaz 2014-7-6

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https://ww2.mathworks.cn/matlabcentral/answers/140602-need-algorithm-to-create-the-list

评论： Fayyaz 2014-7-6

采纳的回答： Image Analyst

Hello,

I need to create a matrix of order 1614006*3, The sequence should be

1st Col (origin) , 2nd Col (Destination) , 3rd Col (Survey_Location)

Origin (1) Destination(1) Survey_Location(1)

Origin (1) Destination(1) Survey_Location(2)

.......

Origin (1) Destination(1) Survey_Location(246)

Origin (1) Destination(2) Survey_Location(1)

...........

Origin (1) Destination(81) Survey_Location(246)

......

Origin (2) Destination(1) Survey_Location(1)

.........

Origin (81) Destination(81) Survey_Location(246)

For this case rows should be 81*81*246=1614006

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Star Strider 2014-7-6

How does this differ from your earlier question: Survey data Matrix arrangement?

Fayyaz 2014-7-6

Hello, it is not different from the previous question. I just posted this question in a more clear way. I am going to delete the previous question.

Thanks.

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Answer 1

Image Analyst 2014-7-6

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编辑：Image Analyst 2014-7-6

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I'm sure there's a more clever vectorized way - Andrei can probably do it in a single line! - but there's always the brute force way:

Origin = randi(9, [81, 1]);
Destination = randi(9, [81, 1]);
Survey_Location = randi(9, [246, 1]);
numOutputRows = size(Origin, 1) * size(Destination, 1) * size(Survey_Location, 1)
output = zeros(numOutputRows, 3);
tic;
row = 1;
for r1 = 1 : size(Origin, 1)  
  for r2 = 1 : size(Destination, 1)
    for r3 = 1 : size(Survey_Location, 1)
      output(row, :) = [Origin(r1), Destination(r2), Survey_Location(r3)];
      row = row + 1;
    end
  end
end
toc

Takes 1.4 second on my computer.

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Image Analyst 2014-7-6

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Oh, I thought you already had some arrays so I just used sample arrays. If you want sequential arrays, you can do

Origin = (1:81)';
Destination = (1:81)';
Survey_Location = (1:246)';

Fayyaz 2014-7-6

Perfect! Actually I am not that much familiar with MATLAB, but I hope I will be able to understand quite soon. Thanks again.

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Answer 2

Andrei Bobrov 2014-7-6

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[z,y,x] = ndgrid(Survey_Location,Destination,Origin);
out = [x(:),y(:),z(:)];

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Image Analyst 2014-7-6

Aha! I knew Andrei could do it in a line or two. He's the master of that.

Fayyaz 2014-7-6

Ya I've realized when Andrei did this.

@Andrei, if possible, kindly look into this question too, you've almost solved it.

http://www.mathworks.com/matlabcentral/answers/140325-matrix-creation-code-problem#answer_143883

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Answer 3

Cedric 2014-7-6

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编辑：Cedric 2014-7-6

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Hello Muhammad,

Here is an example, with 3 elements Origin and Destination, and a 4 elements Survey_Location..

 % - Dummy test case.
 Origin          = 10 : 12 ;
 Destination     = 100 : 102 ;
 Survey_Location = [500, 600, 700, 800] ;
 % - Define columns of final array and concatenate.
 c1 = reshape( repmat( Origin(:)', 3*4, 1 ), [], 1 ) ;
 c2 = repmat( reshape( repmat( Destination(:)', 4, 1 ), [], 1 ), 3, 1 ) ;
 c3 = repmat( Survey_Location(:), 3*3, 1 ) ;
 X  = [c1, c2, c3] ;

Running this, you get