How can I replace values in an array with the value in the previous column's value?

I'm trying to replace a column's value with the previous column's value. Here's my code:

n = [0 0 0 0] %create a matrix with four elements
 %msrd_dist(k) is a new value for each iteration
 for k=1:10
    n(4)=n(3); %wanting to replace a new value with the previous column's value
    n(3)=n(2);
    n(2)=n(1); 
    n(1)=msrd_dist(k);

For example, this is what I want it to do:

fist iteration
   msrd_dist = 15
   n=[15 0 0 0]
second Iteration
   msrd_dist =13
   n=[13 15 0 0]
third iteration
   msrd_dist = 14
   n=[14 13 15 0]
until iteration 10
   msrd_dist = 54
   n=[54 63 52 40]

I am fairly new to Matlab so, any help or suggestions are welcome.

Answer 1

[Jos (10584)]

Somewhat simpler:

n = zeros(1,4) ;                    % array of specific length
while (1)                           % indefinitely, until you hit ctrl-C
    msrd_dist = randi(99) ;         % new value
    n(:) = [msrd_dist n(1:end-1)] ; % shift array, discard last element
    disp(n) ; pause(1) ;            % for display purposes only
end

[Caleb Lindhorst]

This is exactly what I need but when I try to implement the code but modified it to fit my uses and it says "Dimensions of matrices being concatenated are not consistent.

In this code 'num' changes value everytime depending on the length of my data and 'msrd_dist' is the value for the measured distance from my LIDAR.

 num=length(msrd_dist);
 for k=1:num
    n(:) = [msrd_dist n(1:end-1)];

The error says that the dimensions are not consistent. I found an answer online saying to transpose it, I tried that and it is not working.

I have tried a lot of different attempts and nothing is working;

[Jos (10584)]

Apparently msrd_dist is not a scalar (single value), as you originally suggested. Can you give a specific example?

Answer 2

[Star Strider]

Try this:

n(1,:) = [0 0 0 0]; %create a matrix with four elements
L = numel(n);
for k1 = 2:10
    msrd_dist = randi(99)
    n(k1,:) = [0 n(k1-1,1:end-1)] + [msrd_dist zeros(1,L-1)]
end

I have no idea what ‘msrd_dist’ is or does, other than produce a two-digit integer in each iteration. So I use the randi function to simulate it.

[Caleb Lindhorst]

It's a very good attempt but I need to have it stay to a single array so that it is able to run infinitely long.

[Star Strider]

With that specification, try this:

n = [0 0 0 0]; % create a matrix with four elements
L = zeros(1,numel(n)-1);
for k1 = 1:10
    msrd_dist = randi(99)
    n = [0 n(1:end-1)] + [msrd_dist L]
end

Experiment to get the result you want.

[Jos (10584)]

Why the +?

Answer 3

[Caleb Lindhorst]

This is exactly what I would like for it to do.