Select numbers from an array under a specific condition

Dear MATLAB Experts,

Hello. I was curious if I could request for an advice in constructing a program that does the following calculation.

I currently have an array A which contains random integers in numerical order. A = [1 2 4 5 7 9 11 12 13 14 18 23 26 28 32 33 36 37 38 40];

Starting from the first value of array A, I would like to select only the values from A where the selected values are spaced at least 4 numbers. That is, I would like to ultimately obtain A = [1 5 11 18 23 28 33 38] where the selected values from A are such that the numbers between have distances of at least 4.

I would greatly appreciate if you could provide me with any hints in programming this calculation. I am thinking of doing a while loop but having trouble where to start.

Thank you.

Sincerely,

Masato

Answer 1

[Axel Kottgen]

Hi,

You can do a for loop, followed by if to test if the current number in the loop is at least 4 units higher. If that is the case, you save the current number in the loop to a new array (B in my code) which will store your values. I used a variable "c" to store the last saved number, however you could use the last number of B: c=B(length(B))

It gives the current code, with the initial conditions setup:

B=A(1);
c=A(1);
for i=1:length(A)-1,
  if c+4<=A(i+1), 
     B=[B A(i+1)]; 
     c=A(i+1);
end;
end

Note your initial result in your post was incorrect, correct one is here:

B =

       1     5     9    13    18    23    28    32    36    40

[Masato Koizumi]

Thank you Axel Kottgen!! I deeply appreciate your help!