Function that pulls a name from a list at random but doesn't repeat

I'm working on a two-part assignment that requires a function to pick a random index from a list of names. The function itself needs to check if the index has been pulled before so that it doesn't repeat any names. This is what I have so far,

function name = pick_name(list)
  persistent ind_picked

    n_picked = length(ind_picked);
    n_list = length(list);

    if isempty(n_picked) 
        ind = randi(n_list);
        ind_picked = ind;
        name = list(ind);
    else 
        while found == find(ind_picked==ind)
            ind = randi(n_list);    
            ind_picked = [ind_picked,ind];
        end
        name = list(ind);
    end

What am I doing wrong??

[David Fletcher]

You could just use randperm(length(list)) to give you a vector of non-repeating random indices from 1 to the length of the list. You could then just sequentially use the values from this index list

[Matt Rulli]

Unfortunately I am supposed to follow the prescribed steps, but nobody on campus but the professor knows anything about MATLAB, so if you can't catch him in office hours, we're just kind of screwed. I've gotten so much help from this forum, but now the assignments are so complicated I can't even effectively write out what I need help with half the time. The epitome of frustration...

[David Fletcher]

All those variables that you are carefully declaring in the if condition on the first call of the function will go out of scope when the function exits (the condition on the if statement is slightly iffy as well - shouldn't it be if n_picked==0). On the second call because n_picked is persistent and no longer has a length of 0all those variables declared in the if condition won't execute and so ind won't exist when you are trying to use it in the while condition of your else statement (where is found defined btw). It might be worth detailing what your 'prescribed steps' are exactly. It will always be harder to pick a number that doesn't exist in a list of numbers that have already been picked rather than remove a number from a list of numbers that haven't already been picked.

[Matt Rulli]

Answer 1

[David Fletcher]

listNames={'a','b','c','d','e','f','g','n','h'}

for iter=1:9
    name=pick_name(listNames)
end

function name = pick_name(list)

    persistent ind_picked
    candidate=randi(length(list));

    if isempty(ind_picked)
        %Initialize persistent variable with random index
        ind_picked=candidate;
    else
        %look for int that is not already in the list
        while any(candidate==ind_picked)
            candidate=randi(length(list));
        end

        ind_picked=[ind_picked candidate];
    end

    name=list{candidate};

end

Some things you may want to consider and make improvements: something bad happens if you call the function and all items in the list have already been picked. Maybe there should also be a way to 'reset' the function so it forgets it's internal list of picked indexes. Personally, I would also clearly state why this is a bad approach to the problem, and that the while loop could be eliminated, and the code much simplified by instead maintaining a list of indexes that had not been picked.