Switching the elements of an array

hi,

I am plotting data from 2 vectors, the x-axis elements (in a vector called M) needs to be flipped and make the first element 0, the last few elements in M recur like this [1 2 3...500 500 500 500...] and these recurring elements should discarded so it should be [...500 500 500 500 499 498... 3 2 0]

The method I went with is flipping each element by creating a new vector (called N) and using a for loop to switch the order. This however changes the size of my array because it ignores the recurring elements. I want to know how to fix this issue.

My code is

  for k=1:max(M)-1
        N(max(M)-k,:)=k;        
    end
    N(max(M))=0;

The 600x1 M array, becomes a 500x1 N array

*The array M changes because it nested in another loop so I can't use the line for k=1:500

**and I can't use the line for k=1:length(M)-1, because I get the error - Subscript indices must either be real positive integers or logicals.

(Because max(M) = 500 and the length = 600 and N(-100) is not allowed

[John D'Errico]

Please stop re-posting the same question. You have been given good answers. Use of flip is simple, easy to remember, and efficient.

[madhan ravi]

madhan ravi:

Isn’t it straight forward?:

[M(end:-1:2),0]

Ramitha Herath:

I am unfamiliar with that line of code, how does it work?

Also, I get the error -

Error using horzcat

Dimensions of matrices being concatenated are not consistent.

madhan ravi:

size(M) %? what is the size of M ?? is it a vector?
%or try:
MM = M(end:-1:1);
MM(end) = 0

The vector is reversed until the second element and the last element is set as zero (which is the first element in the original vector). You have the code , try it out!

Illustrate with a short 1 by 10 vector of M and N so that it's clear what your desired result should be.

Ramitha Herath:

Thanks for that explanation

Still have the error - Error using horzcat

Dimensions of matrices being concatenated are not consistent

M is a varying size matrix, it is in a nested loop so after each iteration the size changes

Also, I couldn't mention this. The element of N that corresponds to M should be swapped too.

I realized this now after playing with the code. I would really appreciate it if you can tell me what is th best approach? Should I swap the N matrix as well.

In case I didn't word my question properly

N = [A B C ... ZZZ]

M = [1 2 3.. 500 500]

should be swapped to

N = [ZZZ... A B C]

and

M = [500 500 500... 3 2 0]

M vector = [1 2 3 4 5 6 7 8 8 8]

N vector = [10 20 30 40 50 60 70 80 90 100]

Desired Result;

M vector (swapped) = [8 8 8 7 6 5 4 3 2 0]

N vector = [100 90 80 70 60 50 40 30 20 10]

Both vectors should swap

M is a nx1 array, where n is in the range of 500 to 1000

madhan ravi:

M_Swapped = M(end:-1:1);
M_Swapped(end) = 0
N_Swapped = N(end:-1:1)

Ramitha Herath:

This might clear up what I am trying to achieve.

I want that graph to follow the best fit line in blue

If I just swap the x-axis the co-ordinates will get messed up, because the y-co-ordinate points pair up with the wrong x-co-ordinates.

My graph should be the same shape as the best fit line

I have used the below code previously as a temporary ffix, but all that does is flip the axes

 %reverse axes
    set(gca, 'XDir','reverse')
    set(gca, 'XDir','reverse')
    xt = get(gca, 'XTick');
    xtr = linspace(max(xt), min(xt), numel(xt));
    set(gca, 'XTick',xt, 'XTickLabel',sprintfc('%.1f', xtr))
    

Using

M_Swapped = M(end:-1:1);
M_Swapped(end) = 0
N_Swapped = N(end:-1:1)

I end up with the original plot! I feared that would happen.

I need to swap the points such that it gets plotted like this

Answer 1

[Alex Mcaulley]

N = flip(M);
N(end) = 0;

[Hans123]

I couldn't mention this. The element of N that corresponds to M should be swapped too.

I realized this now after playing with the code. I would really appreciate it if you can tell me what is th best approach? Should I swap the N matrix as well.

In case I didn't word my question properly

N = [A B C ... ZZZ]

M = [1 2 3.. 500 500]

should be swapped to

N = [ZZZ... A B C]

and

M = [500 500 500... 3 2 0]

[John D'Errico]

So just swap N AND M. What is the problem? Use of flip will be efficient.