How to obtain the x and y vectors for those whose state is set to i in MATLAB

I have a MATLAB function called nearInfectious2 which represents six people. It takes in parameters of an array of x coordinates, an array of y coordinates, different states relating to those coordinates "s" for susceptible, "i" for infectious and "r" for recovered and lastly a radius. I want to store an array or array(s) of the x and y coordinates for those people whose state is "i". This is what I have thus far, but it is also including the other coordinates which is not what I want. How can I get it to just return arrays with coordinates relating to those whose state is "i"? This is what I have thus far:

[x,y]=nearInfectious2([3,350,150,20,204,103],[92,9,200,5,350,34],["s","i","s","r","i","i"],20);

function [x,y] = nearInfectious2(x,y,states,radius)

for j=1:6

if states(j) == "i"

x(j)=x(j);

y(j)=y(j);

end

end

disp([x])

disp([y])

end

After I have the array of coordinates relating to the people who's states are "i", I want to calculate the distance (using the normal distance formula sqrt((x2 - x1)^2 + (y2 - y1)^2)) between any individuals whose state is "s", to those whose state is "i" to see if it less than radius apart. Any help is greatly appreciated.

[Walter Roberson]

See findgroups and also grpstats and splitapply

Answer 1

[Mehmed Saad]

Your input and output have the same name

Change it

 function [x_out,y_out] = nearInfectious2(x,y,states,radius) 

Initialize a counter in the start of function and increment it whenever state is equal to "i"

For example when j is equal to 2, the condition satisfies so you should write its value at the first index of x_out and y_out and increment counter to 2 after that.

Also you can do this without for loop i,e, using logical indexing

Example

 s = [1 2 1];

if i want to access 1st and 3rd index, i can use direct indexing

 s([1 3])
 ans =

     1     1

or logical indexing

s([true false true])
ans =

     1     1

and getting logic (i.e. i am accessing those values of s which are equal to 1)

s==1
ans =

  1×3 logical array

   1   0   1

and feeding to someother vector of same length or to itself whatever you want

s(s==1)
ans =

   1    1