Extracting elements from a matrix with condition

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Yesbol 2017-4-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/333238-extracting-elements-from-a-matrix-with-condition

编辑： per isakson 2017-4-2

Hello. I have a matrix A 335x5 and I'm extracting 2nd and 3rd column from the matrix with the corresponding number. Currently, the program looks like this:

fileID = fopen('XY_Position.txt','w');
for i=1:nodes
    fprintf(fileID,'%d,%.4f,%.4f\n',i,A(i,2),A(i,3));
end
fclose(fileID);

The output is:

1,355.3035,176.9755
2,353.8089,176.1707
3,352.1992,175.4808
4,350.7045,174.9059
5,344.1509,173.5262
6,338.0571,173.0663
7,332.8832,172.9513
8,330.2387,172.4914
etc

Now I need to include a condition where if, A(current row,4) Not Equal to A(next row,2), then extract elements A(current row,4) and A(current row,5). Please refer to the example below to understand the problem better.

Example, we have a matrix:

305.2889  146.0469  306.5536  142.3677
306.5536  142.3677  301.6096  140.2981
301.6096  140.2981  299.0802  139.0333
299.0802  139.0333  297.0106  138.2285
518.2249  225.1505  507.1871  230.3245
507.1871  230.3245  505.0026  236.7631
505.0026  236.7631  503.5079  239.9825

As can be seen, the element A(current row, 4) is equal to A(next row,2), EXCEPT row 25 and 26.

The output is expected to be:

22,305.2889,146.0469
23,306.5536,142.3677
24,301.6096,140.2981
25,299.0802,139.0333
26,297.0106,138.2285
27,518.2249,225.1505
28,507.1871,230.3245
29,505.0026,236.7631

Please ask questions if problem is not clear enough. Your help is greatly appreciated.

Thank you.