How to change values between two values in an array

I need to replace certain values within an array that fall between 2 and 4. The code should find where the array equals 2 and then find the following location where the array equals 4 and replace all values with 3. Then it should find where the array equals 4 and then find the following location where the array equals 2 and replaces all of those values with 1. And then loop through the array until all values are 1, 2, 3 or 4 and in order (repeats of values are OK).

Here is an example array:

transitions = [1285738, 2, 2, 2915260, 4, 4290129, 2, 5650291, 4, 8030363, 2, 9337983, 4, 12040647];

I need to:

1. change the values that fall between 2 and 4 to 3 (e.g., the 4th, 8th and 12th values should be 3)
2. change the values between 4 and 2 to 1 (e.g., the 6th and 10th values should be 1)

[the cyclist]

Are you saying that the first element will eventually be equal to 1,2,3 or 4? Because I do not see how your transition rules get you there.

[Jake Jordan]

The final result should be:

transitions = [1, 2, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1];

As for the first and last points, I can add a rule to change those. What I'm stuck on though is how to find the points in between 2 and 4 and then in between 4 and 2.

[DGM]

The requirements statement is still ambiguous.

"array equals 2 and ... array equals 4" should become 3

then

"array equals 4 and ... array equals 2" should become 1

If the first operation is performed, then the second condition is never true. If we're to assume that what you mean is that everything in some interval bounded by 2 and 4 is to be converted to 3, and all else is to be converted to 1, then it's still unclear whether 2 or 4 convert to 1 or 3. Your statements say both.

To add to the confusion,

"And then loop through the array until all values are 1, 2, 3 or 4 and in order"

Why would the result still contain 2 or 4? Why would it be in order? What order?

Let's say I assume the following:

values in the closed interval [2 4] become 3

else, they become 1

transitions = [1285738, 2, 2, 2915260, 4, 4290129, 2, 5650291, 4, 8030363, 2, 9337983, 4, 12040647];
ininterval = (transitions>=2) & (transitions<=4);
transitions(ininterval) = 3;
transitions(~ininterval) = 1;

transitions

transitions = 1×14

1 3 3 1 3 1 3 1 3 1 3 1 3 1

If that's not what you're after, you'll have to clarify.

[the cyclist]

I understood @Jake Jordan's rules to be:

1. If a 4 follows a 2, change every intervening value to 3, THEN
2. If a 2 follows a 4, change every intervening value to 1

[DGM]

... oh.

I guess "between" is one of those expressions like "in a row" that are sneakily ambiguous when talking about array structures.

EDIT: oof. I didn't even see OP's comment.

Answer 1

[Swatantra Mahato]

Hi Jake,

I am assuming you want to replace values in the array that occur between a 2 and 4, and those that occur between a 4 and 2.

One way of doing this I can think of is using the "find" function to get the indices of all the 2s and 4s as demonstrated below

transitions = [1285738, 2, 2, 2915260, 4, 4290129, 2, 5650291, 4, 8030363, 2, 9337983, 4, 12040647];
t=find(transitions==2)

t = 1×4

2 3 7 11

f=find(transitions==4)

f = 1×3

5 9 13

you can then loop over 'f' and 't' and replace the values in between accordingly

you can find more information and how-to examples on the "find" function in the documentation

https://www.mathworks.com/help/matlab/ref/find.html

Hope this helps