Can someone tell me what this function actually does?

Question

Hi, I'm new to MATLAB, and I was wondering what this function actually does. The function was copied from a previous question that helped me with the problem of finding the frequency of a number in a string.

Reference: Series of consecutive numbers (different lengths)

d=[3 2 4 2 2 2 3 5 1 1 2 1 2 2 2 2 2 9 2] q = diff([0 d 0] == 2); v = find(q == -1) - find(q == 1); 

Answer 1

Will approach him step by step.

You have an array of d :

 d=[3 2 4 2 2 2 3 5 1 1 2 1 2 2 2 2 2 9 2] 

and you apply to it

 q = diff([0 d 0] == 2); 

This takes the derivative of [0 d 0] == 2 . Basically, it takes the derivative of all numbers that are 2. The result of [0 d 0] == 2 is:

 0 0 1 0 1 1 1 0 0 0 0 1 0 1 1 1 1 1 0 1 0 

You can see that there is 1 when there are 2 in the original vector, and it has 0 in begging and 0 at the end. If we take the derivative of q = diff([0 d 0] == 2) :

 q = 0 1 -1 1 0 0 -1 0 0 0 1 -1 1 0 0 0 0 -1 1 -1 

You get 1 when 2 appears in the original vector and -1 when it disappears. The last line finds only 1 and only -1 separately and subtracts the indices where they appeared, so you can now how many numbers are between them. Since 1 means “the number 2 begins,” and -1 means “no more than 2 lines per line,” this will give you a series length of 2 lines.

 v = find(q == -1) - find(q == 1); v= 1 3 1 5 1 

At the beginning there is one single, then there is a series of 3 2s, then another single, then 5 come and 9 are divided, the last comes.