How to remove some arrays in a matrix

Suppose I have a matrix m:

m = [3;5;6;1;2;8;5;2;9;1;2;7;8;3;4;9;3];

and restricted matrices r1 and r2:

r1 = [5;1;9;3];

r2 = [6;4];

I need a new matrix mm that its included all arrays of matrix m except arrays in matrix r1 and r2:

mm = [2;8;2;2;7;8];

Answer 1

[Star Strider]

You could combine these two lines into one, but I left them separate to make the code more readable:

m = [3;5;6;1;2;8;5;2;9;1;2;7;8;3;4;9;3];
r1 = [5;1;9;3];
r2 = [6;4];
r = [r1; r2];
ml = logical(prod(bsxfun(@ne, r', m),2));
mm = m(ml);

The bsxfun call creates matrices out of ‘r'’ (note transpose) and ‘m’ that are now the same size, then does element-by-element ‘not equal’ operations on them. This creates a logical matrix of (length(m) x length(r)). The prod call then treats the logical values as numeric, multiplies them row-wise to create a column vector with 1 values where the condition is met. It then converts this back to a logical vector to create ‘mm’. The setdiff function would not work here because you want repeated elements, and setdiff does not offer that option. This code does.

EDIT — You changed the question adding ‘r1’ and ‘r2’ (originally just ‘r’) while I was answering this. I updated my answer to reflect that. (The essential code didn’t change.)

[Moe]

Hi and Thanks Star. The edited code gives this error:

Error using prod
PROD is only supported for floating
point input.

[Star Strider]

That code worked perfectly for me (in R2014b), or I’d not have posted it.

Try this:

ml = logical(prod(double(bsxfun(@ne, r', m)),2));

I can’t reproduce your error, so we’ll have to work on this together to get it to run under your version of MATLAB.

[Moe]

New line is works. Thanks. My MATLAB version is 2012a .

[Star Strider]

My pleasure!

I didn’t realise there were such significant version differences in the core functions.

[Moe]

Hi Star,

Matrix r1 and r2 will be updated in each iteration in my code. So, I'm trying to use a cell array for ml and mm as follows:

r{j} = [r1{j}; r2{j}];
ml{j} = logical(prod(double(bsxfun(@ne, r{j}', m),2));
mm{j} = m(ml{j});

But, it gives the following error:

Error using bsxfun
Operands must be numeric arrays.

Can you please help me?

[Star Strider]

I’m not quite certain what your data are, but this works when I test it, with ‘r1’ and ‘r2’ now cell arrays:

r1 = {5;1;9;3};
r2 = {6;4};
r = [r1{:} r2{:}];
ml = logical(prod(double(bsxfun(@ne, r, m)),2));
mm = m(ml);