How can I eliminate unwanted zeros from a matrix?

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Mark 2014-4-24

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评论： Mohamad Mossad 2020-12-16

e.g I want to make this:

1,1,1,1,0,0
1,1,0,0,0,0
1,0,0,0,0,0
1,1,1,1,1,0

into this:

1,1,1,1
1,1
1
1,1,1,1,1
...

Thanks

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Guillaume 2016-6-16

Catherine, please start your own question rather than adding to somebody's else.

Roger Stafford 2016-6-17

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@Catherine: Let A be your original matrix. You can accomplish what you want with:

   T = A~=0;
   n = sum(T,2);
   m = max(n);
   B = nan(size(A,1),m);
   for k = 1:size(A,1)
     B(k,m-n(k)+1:m) = A(k,T(k,:)); % <-- B is the result
   end

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回答（2 个）

Justin 2014-4-24

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编辑：per isakson 2016-6-17

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It depends on what you are trying to end up with exactly but a good approach would be to set all zero values to NaN. NaNs wont show up in plots and you can use nanmean() or other functions which ignore NaNs to work with your matrix. This will also retain the shape of your matrix.

arr = [1 1 0; 1 0 1; 0 0 1];
arr =
     1     1     0
     1     0     1
     0     0     1
arr(arr==0) = nan
arr =
     1     1   NaN
     1   NaN     1
   NaN   NaN     1

Another option is to use a sparse matrix where the memory only retains information about the index of values.

Sparse

   sparse(arr)
ans =
   (1,1)        1
   (2,1)        1
   (1,2)        1
   (2,3)        1
   (3,3)        1

You could even convert the array into a cell array and use cellfun to replace all the zeros with an empty array. It would be much more difficult to operate on the information then though.

What are you trying to accomplish with the data?

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Mohamad Mossad 2020-12-16

Thanks, setting up zeros to nan is a great idea. 6 years later.

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per isakson 2014-4-24

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Hint:

    >> num = [ 1,1,1,1,0,0 ];
    >> num( num == 0 ) = []
    num =
         1     1     1     1

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Image Analyst 2014-4-24

Or the output could be a cell array where you can have different sized rows in each cell. But I don't know why you'd want to mess with that or even want what he's asking for in the first place. Chances are he won't need what he asked for once we learn what he plans on doing with the result.