Change vector if even/odd in a matrix - matlab

Question

I'm new to Matlab programming and I've only had 3 classes so far. I'm having problem with my homework. (Also I am from Iceland so english is not my first language, so please forgive my grammar)
I'm given a matrix, A and I'm supposed to change the value? of a vector to 0 if it is an even number and to 1 if it is an odd number.
This is what I have so far.
A = [90 100 87 43 20 58; 29 5 12 94 8 62; 75 21 36 83 35 24; 47 51 70 59 82 33];
B = zeros(size(A));
for k = 1:length(A)
if mod(A(k),2)== 0 %%number is even
B(k) = 0;
else
B(k) = 1; %%number is odd
end
end
B(A,2==0) = 0;
B(A,2~=0) = 1
What I am getting it this:
B =
0 0 0 0 0 0
1 1 0 0 0 0
1 0 0 0 0 0
1 0 0 0 0 0
1 0 0 0 0 0
If anyone could please help me, it would be greatly appreciated :)

Answer 1

You are very close. Don't use length(A) - use numel(A). length(A) returns the number of elements along the largest dimension. As such, because you have 6 columns and 4 rows, this loop will only iterate 6 times. numel returns the total number of elements in the array A, which is what you want as you want to iterate over each value in A.
Therefore:
A = [90 100 87 43 20 58; 29 5 12 94 8 62; 75 21 36 83 35 24; 47 51 70 59 82 33];
B = zeros(size(A));
for k = 1:numel(A) %// Change
if mod(A(k),2)== 0 %%number is even
B(k) = 0;
else
B(k) = 1; %%number is odd
end
end
The above loop will go through every single element in the matrix and set the corresponding element to 0 if even and 1 if odd.
However, I encourage you to use vectorized operations on your code. Don't use loops for this. Specifically, you can do this very easily with a single mod call:
B = mod(A,2);
mod(A,2) will compute the modulus of every value in the matrix A with 2 as the operand and output a matrix B of the same size. This will exactly compute the parity of each number.
We get for B:
>> A = [90 100 87 43 20 58; 29 5 12 94 8 62; 75 21 36 83 35 24; 47 51 70 59 82 33];
>> B = mod(A,2)
B =
0 0 1 1 0 0
1 1 0 0 0 0
1 1 0 1 1 0
1 1 0 1 0 1