Replacing the zero entry of a vector with its nonzero entries

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Hassan 2018-2-20

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评论： Hassan 2018-2-21

Hello,

Today I have another problem slightly different from my previous question, but they are of the same nature.

Suppose I have a vector A in which there are some zero and nonzero entries. How can I replace the nonzero entries of the vector in such a way that the replacement is done with the closet (left/right index) nonzero entry?

If 0 appears between 2 numbers then we replace it with leftmost nonzero number. For example, if A=[2;0;-1;-2;0;0;4;1], then the replacement is done as follows: the 0 in A(2) is replaced with the number in A(1) (i.e. 2) not A(3); the 0 in A(5) is replaced with the number in A(4) and the zero in A(6) is replaced with the number in A(7).

If it occurs that only 1 entry is nonzero, then we replaced all the zero entries with that nonzero entry. If we have only 2 nonzero entries in the middle of the vector, say k,k+1, then we replaced the 1,2,..,k-1 entries with nonzero entry k,and we replaced the k+2,k+3,...,n with the nonzero entry k+1.

Thank you.

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Jan 2018-2-20

The question is strange. You want to replace the nonzero elements by the closest nonzero elements? The same for: "only 1 entry is nonzero, then we replaced all the nonzero entries with that nonzero entry"?

Do you mean that you want to replace the zeros as in the given example? Please edit the question and fix this.

Hassan 2018-2-20

@Jan Simon, yes you are right. I have edit the question. Thank you for the observation.

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回答（2 个）

Jan 2018-2-20

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https://ww2.mathworks.cn/matlabcentral/answers/383800-replacing-the-zero-entry-of-a-vector-with-its-nonzero-entries#answer_306158

编辑：Jan 2018-2-20

在 MATLAB Online 中打开

I guess, that you want to replace zeros by the nearest non-zero value. Then this is a job for interp1:

z    = (A == 0);
A(z) = interp1(find(~z), A(~z), find(z), 'nearest');

To consider leading and trailing zeros:

A(z) = interp1(find(~z), A(~z), find(z), 'nearest', 'extrap');

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Basil C. 2018-2-21

I guess your latest solution should solve the problem.

Nice approach by using interp1 @Jan Simon. Learnt something new.

Hassan 2018-2-21

I hope so, but I have to analyze it critically.

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Basil C. 2018-2-20

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https://ww2.mathworks.cn/matlabcentral/answers/383800-replacing-the-zero-entry-of-a-vector-with-its-nonzero-entries#answer_306157

编辑：Basil C. 2018-2-20

在 MATLAB Online 中打开

For your first part

 for(i=1:length(A)-1)
    if(A(i)~=0 && A(i+1)==0)
       A(i+1)=A(i);
    end
 end

However I wasn't able to figure out the pattern as to why do you want to set the zero in A(6) to the value in A(8)

For the second part. If the matrix is B.

 % CASE 1
   if(find(B)== length(B)/2+0.5)
       B(:)=B(length(B)/2+0.5);
% CASE 2
   elseif(find(B)== [length(B)/2,length(B)/2+1] )
       B(1:length(B)/2)=B(length(B)/2);
       B(length(B)/2 +1:length(B))=B(length(B)/2+1);
  end