Find elements in a matrix

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Rinu
Rinu 2014-5-31
评论： Rinu 2014-5-31
I have a very large matrix A with 4 columns and hundreds of thousands of rows - the first 3 columns contain x, y and z coordinates and the fourth column contains elevation values. I have another smaller matrix B of 3 columns containing x, y and z coordinates at which I need to extract the elevation values from the larger matrix. How do I search for the particular coordinates (given by B) in the larger matrix A? I tried to use 'find' to extract the indices of every match: >> ind=find(B==A(:,1:3))
but I get the error "Matrix dimensions must agree".

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the cyclist
the cyclist 2014-5-31
编辑：the cyclist 2014-5-31
[tf idx] = ismember(B,A(:,1:3),'rows')
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the cyclist
the cyclist 2014-5-31
编辑：the cyclist 2014-5-31
The second output of the ismember command gives the index to the corresponding row.

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