Deleting specific colums in a matrix

Hello, I´ve got a Matrix M:

1 3 5
2 9 7
4 7 0
3 8 5
3 9 2

How can I delete all colums with a 3 in row1 and a 5 in row3. I`ve tried it like this, but it doesn`t work.

cond1 = M(:,3)=5;
cond2 = M(:,1)=3;
condall = cond1 & cond2
M(condall,:) = [];

Answer 1

[Star Strider]

You need to do the tests in the same statement, because the conditions have to occur simultaneously:

Example —

M = [1 3 5
     2 9 7
     4 7 0
     3 8 5
     3 9 2];

LV = (M(:,1)==3) & (M(:,3)==5);                 % Logical Vector
M(LV,:) = []

M =
     1     3     5
     2     9     7
     4     7     0
     3     9     2

EDIT —

It is also necessary to use the ‘double equal’ ( == ) to test for equality, not a single equal. The ‘single equal’ is an assignment, the ‘double equal’ a test for equality.

[Star Strider]

The problem is that no value in column 1 (or in any other situation) can simultaneously be less than or equal to 2 and greater than or equal to 3.

Example —

M = (1:10)';
Q1 = (M(:,1)>=3) & (M(:,1)<=2)

Q1 =

    10×1 logical array

     0
     0
     0
     0
     0
     0
     0
     0
     0
     0

If you reverse the conditions, you will get a valid logical vector:

Q2 = (M(:,1)>=2) & (M(:,1)<=3)

Q2 =

    10×1 logical array

     0
     1
     1
     0
     0
     0
     0
     0
     0
     0

So, with your matrix ‘M’:

M = [1 3 5
     2 9 7
     4 7 0
     3 8 5
     3 9 2];

LV = (M(:,1)>=2) & (M(:,1)<=3) & (M(:,3)==5);                 % Logical Vector
M(LV,:) = []

M =

       1     3     5
       2     9     7
       4     7     0
       3     9     2

This is the same as the previous result.

Answer 2

[Hans Bauer]

Great. That works. Thanks a lot. By the way I`ve got another question: How does it works, when I have 3 conditions: I want to delete all colums when the number in row1 is >=3 and the number in row1 is <= 2 and when there is a 5 in row3. I tried this, but it doesn`t work.

LV = (M(:,1)>=3) & (M(:,1)<=2) &  (M(:,3)==5);
M(LV,:) = [];

[Akira Agata]

"the number in row1 is >=3 and the number in row1 is <= 2" ? That should be always false. Is this an editorial mistake ?

[Star Strider]

I addressed that in my Comment to my Answer, rather than a Comment here.

Answer 3

[Andrei Bobrov]

out = M(~ismember(M(:,[1,3]),[3,5]),:);