How to choose a random value from an array?

Hi,

I have an array of values and I need to frame an expression such that it chooses the value from the array automatically instead of me assigning a value from the array everytime. For example, if

A_index=[1 2 3 4]

B_index=[5 6 7 8]

while initialising A, B for the first time I choose A=2, and B=6 (A and B are selected with corresponding element) and next time A=4, B=8

However, I have used this coding

 A=@(A_index) A_index(ceil(rand*length(A_index)))
 B=@(B_index) B_index(ceil(rand*length(B_index)))

But this line doesn't generate a value, instead it returns the expression itself. Why is that so?

Could someone please help me.

[dpb]

A=@(A_index) A_index(ceil(rand*length(A_index)))

...this line doesn't generate a value, instead it returns the expression itself. Why is that so?

Because you defined A and B to be function handles.

Perhaps you're looking for something like

A=A_index(randperm(length(A_index),1));

maybe???

[Priya]

No, its inconsistent. I mean sometimes it works but for other iteration when A=4, I get B as 7 instead of 8.

Answer 1

[dpb]

Then you must want to only generate a single index instead of two and use it for both--

idx=randperm(length(A_index),1);
A=A_index(idx);
B=B_index(idx);

[Priya]

Perfect! Thanks very much.

Answer 2

[Image Analyst]

How about

randomIndex = randi(length(A), 1)
selected_A_value = A(randomIndex)

Repeat for B after changing the A's to B's.

[Zohaib Leghari]

It selects single value from the array A

How to randomly select the multiple values from the array A and B?

[dpb]

Change the number of elements generated in the randi function in IA's way or the number of the permuations returned in my solution above. Depends upon whether the two are correlated as the original poster wanted as to which is the one you want.

And, of course, whether you use a random permutation of the indices 1:N or generate a realization of M integers over ranged of 1:N is also immaterial, both use the underlying pseudorandom number generator. Altho it has been around now for quite a long time, randi is a more recent introduction to MATLAB than randperm and I'm an old geezer so I tend to forget about it.

[Image Analyst]

M = 20; % Whatever you want.
randomIndexes = randperm(length(A), M) % Get M random indexes.
selected_A_values = A(randomIndexes)
randomIndexes = randperm(length(B), M) % Get M random indexes.
selected_B_values = B(randomIndexes)