How do I combine two index vectors to form a 2D index matrix?

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Dean Ranmar 2016-12-20

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https://ww2.mathworks.cn/matlabcentral/answers/317561-how-do-i-combine-two-index-vectors-to-form-a-2d-index-matrix

编辑： Jan 2016-12-26

采纳的回答： Jan

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I have two methods for identifying which elements in a matrix have certain properties (e.g.; exceed a threshold).

ndx = Amat > THR; % matrix of threshold crossing locations

and:

[rdx, cdx] = find(Amat>THR); % vectors of threshold crossing locations

that I use for two different purposes [and actually apply to different matrices.] Results from the two methods are compared eventually. I'd like to take the two vectors (rdx, cdx) and convert them to a matrix so I can do an operation such as:

Adx = Amat(ndx); % matrix of threshold crossing amplitudes

which is done for the former case. I'm sure there's a simple way to take the two vectors and combine them to produce "pointer" matrix "ndx," but I haven't found it.

Help?

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Dean Ranmar 2016-12-20

Of course "ndx" is a true/false matrix of same dimension as matrix Amat.

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Jan 2016-12-20

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https://ww2.mathworks.cn/matlabcentral/answers/317561-how-do-i-combine-two-index-vectors-to-form-a-2d-index-matrix#answer_247903

编辑：Jan 2016-12-26

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Does not look elegant:

[rdx, cdx] = find(Amat > THR);
Index      = sub2ind(size(Amat), rdx, cdx);  % [EDITED, was ind2sub...]
ndx        = false(size(Amat));
ndx(Index) = true;