MATLAB: How to extract specific rows from one array to another array

arraycopyextractfilterintersect

Hi. I have these two arrays:

NA2 =

         0    0.9800    1.0000    0.0200   -3.1000    1.0000    1.0000
    0.1000    0.9800    0.0591    0.0200   -3.0000    1.0000    0.0779
    0.2000    0.9800    0.0591    0.0200   -2.9000    1.0000    0.0779
    0.3000    0.9800    0.0591    0.0200   -2.8000    1.0000    0.0779
    0.4000    0.9800    0.0591    0.0200   -2.7000    1.0000    0.0779
    0.5000    0.9800    0.0591    0.0200   -2.6000    1.0000    0.0779
    0.6000    0.9800    0.0591    0.0200   -2.5000    1.0000    0.0779
    0.7000    0.9800    0.0591    0.0200   -2.4000    1.0000    0.0779
    0.8000    0.9800    0.0591    0.0200   -2.3000    1.0000    0.0779
    0.9000    0.9800    0.0591    0.0200   -2.2000    1.0000    0.0779
    1.0000    0.9800    0.0591    0.0200   -2.1000    1.0000    0.0779
    1.1000    0.9800    0.0591    0.0200   -2.0000    1.0000    0.0779
    1.2000    0.9800    0.0300    0.0200   -1.9000    1.0000    0.0494
    1.3000    0.9800    0.0300    0.0200   -1.8000    1.0000    0.0494
    1.4000    0.9800    0.0300    0.0200   -1.7000    1.0000    0.0494
    1.5000    0.9800    0.0300    0.0200   -1.6000    1.0000    0.0494
    1.6000    0.9800    0.0300    0.0200   -1.5000    1.0000    0.0494
    1.7000    0.9800    0.0300    0.0200   -1.4000    1.0000    0.0494
    1.8000    0.9800    0.0300    0.0200   -1.3000    1.0000    0.0494
    1.9000    0.9800    0.0300    0.0200   -1.2000    1.0000    0.0494
    2.0000    0.9800    0.0300    0.0200   -1.1000    1.0000    0.0494
    2.1000    0.9800    0.0009    0.0200   -1.0000    1.0000    0.0209
    2.2000    0.9800         0    0.0200   -0.9000    1.0000    0.0200
    2.3000    0.9800         0    0.0200   -0.8000    1.0000    0.0200
    2.4000    0.9800         0    0.0200   -0.7000    1.0000    0.0200
    2.5000    0.9800    0.0009    0.0200   -0.6000    1.0000    0.0209
    2.6000    0.9800    0.0009    0.0200   -0.5000    1.0000    0.0209
    2.7000    0.9800    0.0009    0.0200   -0.4000    1.0000    0.0209
    2.8000    0.9800         0    0.0200   -0.3000    1.0000    0.0200
    2.9000    0.9800         0    0.0200   -0.2000    1.0000    0.0200
    3.0000    0.9800    0.0009    0.0200   -0.1000    1.0000    0.0209
    3.1000    0.9800         0    0.0200   -0.0000    1.0000    0.0200
    3.2000    0.9800         0    0.0200    0.1000    0.0591    0.0012
    3.3000    0.9800         0    0.0200    0.2000         0         0
    3.4000    0.9800         0    0.0200    0.3000         0         0
    3.5000    0.9800         0    0.0200    0.4000    0.0591    0.0012
    3.6000    0.9800         0    0.0200    0.5000         0         0
    3.7000    0.9800         0    0.0200    0.6000    0.0591    0.0012
    3.8000    0.9800         0    0.0200    0.7000         0         0
    3.9000    0.9800         0    0.0200    0.8000         0         0
    4.0000    0.9800         0    0.0200    0.9000    0.0591    0.0012
    4.1000    0.9800         0    0.0200    1.0000         0         0
    4.2000    0.9800         0    0.0200    1.1000    0.0591    0.0012
    4.3000    0.9800         0    0.0200    1.2000         0         0
    4.4000    0.9800         0    0.0200    1.3000         0         0
    4.5000    0.9800         0    0.0200    1.4000         0         0
    4.6000    0.9800         0    0.0200    1.5000         0         0
    4.7000    0.9800         0    0.0200    1.6000    0.0300    0.0006
    4.8000    0.9800         0    0.0200    1.7000         0         0
    4.9000    0.9800         0    0.0200    1.8000         0         0
    5.0000    0.9800         0    0.0200    1.9000         0         0
    5.1000    0.9800         0    0.0200    2.0000         0         0
    5.2000    0.9800         0    0.0200    2.1000    0.0009    0.0000
    5.3000    0.9800         0    0.0200    2.2000         0         0
    5.4000    0.9800         0    0.0200    2.3000         0         0
    5.5000    0.9800         0    0.0200    2.4000         0         0
    5.6000    0.9800         0    0.0200    2.5000         0         0
    5.7000    0.9800         0    0.0200    2.6000    0.0009    0.0000
    5.8000    0.9800         0    0.0200    2.7000         0         0
    5.9000    0.9800         0    0.0200    2.8000         0         0
    6.0000    0.9800         0    0.0200    2.9000         0         0
    6.1000    0.9800         0    0.0200    3.0000         0         0
    6.2000    0.9800         0    0.0200    3.1000         0         0

CapacityOut =

Now, I am trying to "filter" NA2 using the values in CapacityOut. Meaning, I would like to extract rows which has the value of CapacityOut in the first column then output the new array to NA3.

I have this code which does the extraction:

    z=0;
for i=1:size(NA2,1)
    for j=1:size(CapacityOut,1)
        if NA2(i,1)==CapacityOut(j,1)
            z=z+1;
            NA3(z,:)=NA2(i,:);
        else
        end
    end
end

However, this is the result:

NA3 =

         0    0.9800    1.0000    0.0200   -3.1000    1.0000    1.0000
    1.1000    0.9800    0.0591    0.0200   -2.0000    1.0000    0.0779
    2.0000    0.9800    0.0300    0.0200   -1.1000    1.0000    0.0494
    4.2000    0.9800         0    0.0200    1.1000    0.0591    0.0012
    6.2000    0.9800         0    0.0200    3.1000         0         0

It did not copy the rows with 3.1000 and 5.1000 on the first column. I have tried it on another set of array but with whole numbers on the first column and it works perfectly. Do you have any idea why?

Best Answer

The problem is that you test for equivalence of floating point values. This is bound to cause errors, as has been discussed hundreds of times on this forum:

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

https://www.mathworks.com/matlabcentral/answers/350303-why-0-6-is-not-equal-to-0-2-3

http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

etc., etc.

The solution is to use ismembertol, or compare the absolute difference against some tolerance value:

idx = false(size(NA2,1),1);
tol = 0.0001;
for k = 1:size(CapacityOut,1)
   idx = idx | abs(NA2(:,1)-CapacityOut(k))<tol;
end
out = NA2(idx,:);

giving:

>> out
out =
   0.00000   0.98000   1.00000   0.02000  -3.10000   1.00000   1.00000
   1.10000   0.98000   0.05910   0.02000  -2.00000   1.00000   0.07790
   2.00000   0.98000   0.03000   0.02000  -1.10000   1.00000   0.04940
   3.10000   0.98000   0.00000   0.02000  -0.00000   1.00000   0.02000
   4.20000   0.98000   0.00000   0.02000   1.10000   0.05910   0.00120
   5.10000   0.98000   0.00000   0.02000   2.00000   0.00000   0.00000
   6.20000   0.98000   0.00000   0.02000   3.10000   0.00000   0.00000
>>

Related Solutions

MATLAB: How to make a permanent change to a matrix using sortrows

 P = sortrows(P,7) ;

Most of the time functions don't operate "externally", so SORTROWS doesn't alter your array P defined in the workspace. It creates a new sorted array that it outputs. You have to store this output back into P if you want P to be the sorted version. If you wanted to keep the original, you could store it into a new variable:

 P_sorted = sortrows(P,7) ;

MATLAB: How to compare the elements of a matrix and fill another matrix with the elements of a vector

Since your t matrix is full of 0 and 1 you can take advantage of that and just do this

a = [0.9 0.8 0.7 0.6 0.5];
b = [0.1 0.2 0.3 0.4 0.5];
t = ff2n(n);
t1 = t.*a
t1 =
         0         0         0         0         0
         0         0         0         0    0.5000
         0         0         0    0.6000         0
         0         0         0    0.6000    0.5000
         0         0    0.7000         0         0
         0         0    0.7000         0    0.5000
         0         0    0.7000    0.6000         0
         0         0    0.7000    0.6000    0.5000
         0    0.8000         0         0         0
         0    0.8000         0         0    0.5000
         0    0.8000         0    0.6000         0
         0    0.8000         0    0.6000    0.5000
         0    0.8000    0.7000         0         0
         0    0.8000    0.7000         0    0.5000
         0    0.8000    0.7000    0.6000         0
         0    0.8000    0.7000    0.6000    0.5000
    0.9000         0         0         0         0
    0.9000         0         0         0    0.5000
    0.9000         0         0    0.6000         0
    0.9000         0         0    0.6000    0.5000
    0.9000         0    0.7000         0         0
    0.9000         0    0.7000         0    0.5000
    0.9000         0    0.7000    0.6000         0
    0.9000         0    0.7000    0.6000    0.5000
    0.9000    0.8000         0         0         0
    0.9000    0.8000         0         0    0.5000
    0.9000    0.8000         0    0.6000         0
    0.9000    0.8000         0    0.6000    0.5000
    0.9000    0.8000    0.7000         0         0
    0.9000    0.8000    0.7000         0    0.5000
    0.9000    0.8000    0.7000    0.6000         0
    0.9000    0.8000    0.7000    0.6000    0.5000
t2 = not(t.*a).*b
t2 =
    0.1000    0.2000    0.3000    0.4000    0.5000
    0.1000    0.2000    0.3000    0.4000         0
    0.1000    0.2000    0.3000         0    0.5000
    0.1000    0.2000    0.3000         0         0
    0.1000    0.2000         0    0.4000    0.5000
    0.1000    0.2000         0    0.4000         0
    0.1000    0.2000         0         0    0.5000
    0.1000    0.2000         0         0         0
    0.1000         0    0.3000    0.4000    0.5000
    0.1000         0    0.3000    0.4000         0
    0.1000         0    0.3000         0    0.5000
    0.1000         0    0.3000         0         0
    0.1000         0         0    0.4000    0.5000
    0.1000         0         0    0.4000         0
    0.1000         0         0         0    0.5000
    0.1000         0         0         0         0
         0    0.2000    0.3000    0.4000    0.5000
         0    0.2000    0.3000    0.4000         0
         0    0.2000    0.3000         0    0.5000
         0    0.2000    0.3000         0         0
         0    0.2000         0    0.4000    0.5000
         0    0.2000         0    0.4000         0
         0    0.2000         0         0    0.5000
         0    0.2000         0         0         0
         0         0    0.3000    0.4000    0.5000
         0         0    0.3000    0.4000         0
         0         0    0.3000         0    0.5000
         0         0    0.3000         0         0
         0         0         0    0.4000    0.5000
         0         0         0    0.4000         0
         0         0         0         0    0.5000
         0         0         0         0         0
t1+t2
ans =
    0.1000    0.2000    0.3000    0.4000    0.5000
    0.1000    0.2000    0.3000    0.4000    0.5000
    0.1000    0.2000    0.3000    0.6000    0.5000
    0.1000    0.2000    0.3000    0.6000    0.5000
    0.1000    0.2000    0.7000    0.4000    0.5000
    0.1000    0.2000    0.7000    0.4000    0.5000
    0.1000    0.2000    0.7000    0.6000    0.5000
    0.1000    0.2000    0.7000    0.6000    0.5000
    0.1000    0.8000    0.3000    0.4000    0.5000
    0.1000    0.8000    0.3000    0.4000    0.5000
    0.1000    0.8000    0.3000    0.6000    0.5000
    0.1000    0.8000    0.3000    0.6000    0.5000
    0.1000    0.8000    0.7000    0.4000    0.5000
    0.1000    0.8000    0.7000    0.4000    0.5000
    0.1000    0.8000    0.7000    0.6000    0.5000
    0.1000    0.8000    0.7000    0.6000    0.5000
    0.9000    0.2000    0.3000    0.4000    0.5000
    0.9000    0.2000    0.3000    0.4000    0.5000
    0.9000    0.2000    0.3000    0.6000    0.5000
    0.9000    0.2000    0.3000    0.6000    0.5000
    0.9000    0.2000    0.7000    0.4000    0.5000
    0.9000    0.2000    0.7000    0.4000    0.5000
    0.9000    0.2000    0.7000    0.6000    0.5000
    0.9000    0.2000    0.7000    0.6000    0.5000
    0.9000    0.8000    0.3000    0.4000    0.5000
    0.9000    0.8000    0.3000    0.4000    0.5000
    0.9000    0.8000    0.3000    0.6000    0.5000
    0.9000    0.8000    0.3000    0.6000    0.5000
    0.9000    0.8000    0.7000    0.4000    0.5000
    0.9000    0.8000    0.7000    0.4000    0.5000
    0.9000    0.8000    0.7000    0.6000    0.5000
    0.9000    0.8000    0.7000    0.6000    0.5000

Best Answer

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MATLAB: How to make a permanent change to a matrix using sortrows

MATLAB: How to compare the elements of a matrix and fill another matrix with the elements of a vector

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