MATLAB: How to delete zeros from a vector and place it again in that vector

matrixzeros

I have a vector like,

A = [2000 -1000 0 0 0 2000 -1000 0 0 0 2000 -1000 0 0 0 1000]';

For removing zeros, I did,

B = A(A ~= 0);

Now, I want the same vector A from B. Is there any MATLAB functions available or I need to code it?

Thank you.

Best Answer

Once you've thrown away the zeros, they're gone -- there's no way of knowing where they were in the original A from B alone.

To do this you'll have to save the locations of the zeros in A (or non-zero, one is just the complement of the other) as well as total length in order to rebuild the vector from the pieces.

iNZ=find(A);          % nonzero locations in A
lA=length(A);         % total length

with those additional pieces of information and B, then

A=zeros(1,lA); A(iNZ)=B;

will reproduce A. But, again, w/o the additional info it's not possible to rebuild A precisely; too little information remains.

ADDENDUM

Actually, you can do it with only one additional variable; if you save the logical array instead of the locations only, then you have the length of the original array implicitly.

iNZ=(A~=0);       % logical array instead of vector of locations

then, having B and iNZ

A(iNZ)=B;

will reconstruct A. Of course, since size(iNZ) == size(A), you might as well just save A to begin with. :)

Related Solutions

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

MATLAB: How to chose random row which contain non-zero element

I would first find the non-zero rows, then choose randomly amongst them:

nzr = find(sum(A,2)>0);                             % Indices Of Non-Zero Rows
random_nz_row = nzr(randi(length(nzr), 1))          % Choose One Non-Zero Row
nz_row = A(random_nz_row,:)                         % Display Random Non-Zero Row

Best Answer

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

MATLAB: How to chose random row which contain non-zero element

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