Writing to file with condition

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.

For instance, we have a matrix:

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

Answer 1

[Guillaume]

I would just construct the matrix to be printed according to your rule, then write it in one go to file. If I understood correctly:

A = [22.0000  305.2889  146.0469  306.5536  142.3677
     23.0000  306.5536  142.3677  301.6096  140.2981
     24.0000  301.6096  140.2981  299.0802  139.0333
     25.0000  299.0802  139.0333  297.0106  138.2285
     26.0000  518.2249  225.1505  507.1871  230.3245
     27.0000  507.1871  230.3245  505.0026  236.7631
     28.0000  505.0026  236.7631  503.5079  239.9825];

B = sortrows([A(:, 1:3); A(A(1:end-1, 4) ~= A(2:end, 2), [1, 4, 5]) + [0.5, 0, 0]]);  %requires R2016b or later
B(:, 1) = B(1, 1) + (0 : size(B, 1)-1);
csvwrite('XY_Position.txt', B);

[Yesbol]

It perfectly works for the matrix provided. However, when I try to sort bigger matrix, like in my case 343x5, it gives me :

Error using  + 
Matrix dimensions must agree.

Thank you

[Guillaume]

Hum, there's only two + operations:

• A(expression, [1, 4, 5])) + [0.5, 0, 0], adds a matrix of unknown height with 3 columns to a 3 columns vector. This is guaranteed to succeed in R2016b or later.
• B(1, 1) + (0 : size(B, 1)-1), addition of a scalar and a vector. Will always succeed.

You must have modified something in one of the expressions to make it fail. If not, can you attach your matrix.

[Yesbol]

I'm attaching you my matrix.

[Guillaume]

As expected, works without issues for me with this new matrix.

You are using R2016b or R2017a, right? On R2016a or earlier the first addition would result in 'matrix dimension must agree error'. In which case,

B = sortrows([A(:, 1:3); bsxfun(@plus, A(A(1:end-1, 4) ~= A(2:end, 2), [1, 4, 5]), [0.5, 0, 0])]);  %any version

would fix the problem. But then, the demo wouldn't have worked either.

[Yesbol]

It's working! Thank you!