How to fill end of rows of a matrix with NaN values?

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Mr M. 2021-6-1

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回答： Walter Roberson 2021-6-2

I have a matrix M, and vector of indices K. I would like to make an element M(k,j) = NaN if j >= K(k). It is possible to do this with a vectorized short methode?

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Bob Thompson 2021-6-1

编辑：Bob Thompson 2021-6-1

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Why not just preallocate the matrix with nan values? Do you have any idea of the max size your matrix could be?

M = nan(max(k),max(j));

Mr M. 2021-6-2

I think, you misunderstood my problem. Lets see an example.

let M be: [1,2,3; 1,2,3; 1,2,3; 1,2,3]; An let K be: [2; 3; 1; NaN or 4 or anithing else]. This means I need the following output:

[1;NaN,NaN; 1,2,NaN; NaN,NaN,NaN; 1,2,3]

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Answer 1

Sulaymon Eshkabilov 2021-6-1

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Hi,

here is a simple solution, e.g.:

M = magic(5);
M(:,end)=nan

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Answer 2

Walter Roberson 2021-6-2

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M = [1,2,3; 1,2,3; 1,2,3; 1,2,3]
M = 4×3
     1     2     3
     1     2     3
     1     2     3
     1     2     3
K = [2; 3; 1; NaN]
K = 4×1
     2
     3
     1
   NaN
M((1:size(M,2)) >= K(:)) = nan
M = 4×3
     1   NaN   NaN
     1     2   NaN
   NaN   NaN   NaN
     1     2     3