Insert rows in a matrix

Question

Ionut Anghel 2015-6-24

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评论： David Verrelli 2018-3-27

Hi, I have the following problem: matrix

AA=[NaN 1 2 3 4 5
            NaN 10 20 30 40 50
            ...............
            NaN 1E8 2E8 3E8 4E8 5E8 ];

There is possible to insert every 10 row the following row:

[NaN NaN 99 Nan 77 NaN];

without a loop?

Thank you

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Answer 1

Guillaume 2015-6-24

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One way of doing this:

%work out how to split AA
rowdist = ones(1, ceil(size(AA, 1) / 10)) * 10;
rowdist(end) = 10 + mod(size(AA, 1), -10);
%do the splitting and transpose into a row
splitAA = mat2cell(AA, rowdist, size(AA, 2))';
%add another row with the data to insert
splitAA(2, :) = {[NaN NaN 99 NaN 77  NaN]};
%avoid insertion of the new row at the end if the height 
%of the matrix is not a multiple of ten
if mod(size(AA, 1), 10)
   splitAA{2, end} = [];
end
%join it all together
newAA = vertcat(splitAA{:})

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Ionut Anghel 2015-6-24

Very nice method! Thank you.

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Answer 2

Anthony Poulin 2015-6-24

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编辑：Anthony Poulin 2015-6-24

在 MATLAB Online 中打开

You can try something like this (with B = [NaN NaN 99 Nan 77 NaN]):

 for i=10:10:100  
    AA = [AA(1:i, 1:end); B; AA(i+1:end,1:end)];
 end

(100 is an arbitrary value)

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Anthony Poulin 2015-6-24

Or just replacing "i" by "i + i/10 -1".

David Verrelli 2018-3-27

Or run the loop 'backwards', as in for i=100:-10:10 (although 100 might not be the correct terminal value for your case, as already noted). Even though the matrix is still resized at each step, at least this way the subsequent changes aren't affected by previous steps.

BTW, "1:end" can just be replaced with ":" alone.

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