Create a matrix on the basis of other matrix

Hi given a vector

SPI= [2 3 4 8 11 13 14 15 16 19 20];

and the array

AA= [1 2  3  4  0   11    15;
    0  0  0  8  13  16     0;
    0  0  0  0  0   18     0;
    0  0  0  0  0   19     0;
    0  0  0  0  0   20     0];

I want to create a matrix DD that is AA but with just the element inside SPI. So:

DD = [ 2  3  4  0   11    15;
       0  0  8  13  16     0;
       0  0  0  0   0     0;
       0  0  0  0   19     0;
       0  0  0  0   20     0];
   

may someone help me?

[Walter Roberson]

I notice that you delete the first column of AA as it is left without any elements from SPI. Why are you not also deleting the all-zero row 3 ? Or if the rule is that the first row has to contain an element from SPI, why are you not deleting the column [0; 13; 0; 0; 0] ? What are the rules?

[luca]

the array SPI could vary and contain all the elements of AA, that instead is fixed. So depending on the value inside SPI I want to derive DD.

Sorry for the third column, was my mistake! now it's fixed

Answer 1

[Fabio Freschi]

% your data
SPI = [2 3 4 8 11 13 14 15 16 18 19 20];
AA = [1 2  3  4  0   11  14  15;
0  0  0  8  13  16  0   0;
0  0  0  0  0   0  0   0;
0  0  0  0  0   19  0   0;
0  0  0  0  0   20  0   0];
% mask
iMask = ismember(AA,SPI);

% matrix DD with zeros
DD = AA.*iMask;

% now you can filter out the rows and cols of all zeros
DD = DD(:,any(iMask,1));   % cols filter
DD = DD(any(iMask,2),:);   % rows filter

[luca]

what is ii?

[Fabio Freschi]

imask, sorry changed the name to make it more clear but I didn't check for possible typos. Now I fixed the post

[luca]

give me this error

The logical indices in position 1 contain a true value outside of the array bounds.

Error 
DD = DD(any(iMask,1),:);   % cols filter

[Fabio Freschi]

You are not running the last checked version. Retry with the code available now. Sorry for the confusion

[Walter Roberson]

Fabio's suggested code will eliminate the row 0 0 0 0 0 0;

I do not understand at the moment why that row is being kept in the desired solution.

[Fabio Freschi]

Me neither! but I kept all steps separated to that the OP can pick the parts of his choice