Exclude elements from array

Question

I have a column vector:

A = [1; 2; 3; 4; 4; 5; 5; 7];

I wish to exclude the elements of A that are in a second matrix B:

B = [4; 5]

The final result should be:

A = [1; 2; 3; 7]

I am pretty sure using MATLAB elegant syntaxing, this be accomplished without writing a for loop, but not sure how?

possible duplicate of [How do I remove elements at a set of indices in a vector in MATLAB?](http://stackoverflow.com/questions/3789847/) and [Retrieving the elements of a matrix with negated exact indexing with index matrix?](http://stackoverflow.com/questions/13918790/) — Eitan T, May 29 '13 at 14:31
Note that `'` is the (complex conjugate) transpose function. So you should use a different letter for your second matrix. — Dennis Jaheruddin, May 29 '13 at 14:32
Sorry, my bad. This is not a duplicate, I thought the second matrix holds indices to the rows to be removed, but it contains the elements themselves. — Eitan T, May 29 '13 at 14:42

score 20 · Accepted Answer · answered May 29 '13 at 14:35

20

I would use Afilt=A(~ismember(A,B));. This will return all elements of A which are not in B.

answered May 29 '13 at 14:35

Marc Claesen

4

Alternatively: `A(ismember(A,B))=[];` – Mohsen Nosratinia May 30 '13 at 11:28

Eitan T · Answer 2 · 2013-05-29T16:38:35.890

6

You can compare values with bsxfun:

A = A(all(bsxfun(@ne, A(:), B(:).'), 2))

This approach is especially good if you need to handle floating-point numbers (whereismember fails):

A(all(abs(bsxfun(@minus, A(:), B(:).')) >= eps, 2))

Instead of eps, you can set any tolerance threshold you want.

edited May 29 '13 at 16:38

answered May 29 '13 at 14:40

Eitan T

1

If you want to preserve the order, use `setOrder`= `'stable'` as additional input – Dennis Jaheruddin May 29 '13 at 14:44
1

using setdiff you loose multiplicity of elements. – Mohsen Nosratinia May 29 '13 at 16:19
@MohsenNosratinia Absolutely correct, haven't thought about it. – Eitan T May 29 '13 at 16:31

Dennis Jaheruddin · Answer 3 · 2013-05-29T14:40:39.233

2

EDIT: If you want to remove row 4 and 5 it is this, if you want to remove the rows with fours and fives check the other answers.

Simple as this

A = [1; 2; 3; 4; 4; 5; 5; 7];     
B = [4; 5];

A(B)=[];

edited May 29 '13 at 14:40

answered May 29 '13 at 14:32

Dennis Jaheruddin

2

I think you got the question wrong (like I did). You are supposed to remove the values 4 and 5, not rows 4 and 5. – Eitan T May 29 '13 at 14:44
@EitanT I have edited accordingly. Not sure whether we misread or whether the information was added. – Dennis Jaheruddin May 29 '13 at 14:45
I think we were mislead by the wording of the question. – Eitan T May 29 '13 at 15:27

3 Answers3