Interleaving Vectors in MATLAB

We have a question to interleave two vectors using a for loop:

For this problem you have to modify the code in your file so that, using a for-loop, you interleave the elements of A and B creating a new vector called C. You can assume that A and B are the same length.

Testing

For this question you should, in a text file called, q2c.txt write a table containing three new test cases. As a reference example, two possible test cases for this are:

A B C

[1 2 4] [5 6 7] [1 5 2 6 4 7]

[-1 0 2] [7 3 1] [-1 7 0 3 2 1]

Coding

Now code your solution to the problem above in your q2c.m file. Make sure you include some code at the end to display the vector C after the loop has finished running.

[Steven Lord]

Since this sounds like a homework assignment, please show us what you've done so far to try to solve the problem and ask a specific question about where you're having difficulty and we may be able to provide some guidance.

Answer 1

[Andrei Bobrov]

Without loop:

A = [1 2 4];B =  [5 6 7];

C = [A;B];
C = C(:)';

with loop:

for ii = numel(A):-1:1
    C(2*ii-[0 1]) = [B(ii),A(ii)];
end

[David Kellie]

Our question asks for a for loop. Can you provide an answer with a for loop?

[Rik]

The loop version lacks pre-allocation (which is mostly dealt with by looping backward). However, this will still cause an issue if C already exists. The code below makes more sense to me.

C=zeros(1,2*numel(A));
for ii = 1:numel(A)
    C(2*ii-[1 0]) = [A(ii),B(ii)];
end

Answer 2

[Abiy Tsegaye Demissie]

What a coincidence because I had the same question for my practical assignment.

So what I did was I used a for loop then used an if statement.

A=[1 3 5];
B=[2 4 6];
C=[ ];

for i = 1:length(A)    %I am not sure about the length but it seems to work
    if A(i)~=B(i)
        C = [C A(i) B(i)];
    end

    if A(i)==B(i)        %This is to ensure that it also works for vectors with the same numbers
        C = [C A(i) B(i)];
    end
end

disp(C)

Result 1     2     3     4     5     6

This is the best I can do. I do not know if there is a better way of doing this using a for loop. This seems to work well.

[Rik]

The length function should avoided. Either use numel, or use size(___,dim). Also, you don't need the comparison, you always need to do the same. If you did need the comparison, it would be clearer if you used an else instead of a new if with the inverted test.

[Safwan]

Thanks for the tips guys. I was struggling to do this for my prac.