How to choose a random value from an array?

Question

Priya 2014-6-8

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/133322-how-to-choose-a-random-value-from-an-array

评论： Image Analyst 2021-1-29

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.

2 个评论
显示无隐藏无

dpb 2014-6-9

在 MATLAB Online 中打开

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 2014-6-9

编辑：Priya 2014-6-9

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

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

dpb 2014-6-9

4
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/133322-how-to-choose-a-random-value-from-an-array#answer_140079

在 MATLAB Online 中打开

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);

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Priya 2014-6-9

Perfect! Thanks very much.

请先登录，再进行评论。

Answer 2

Image Analyst 2014-6-9

5
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/133322-how-to-choose-a-random-value-from-an-array#answer_139981

在 MATLAB Online 中打开

How about

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

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

3 个评论
显示 1更早的评论隐藏 1更早的评论

dpb 2021-1-28

编辑：dpb 2021-1-28

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 2021-1-29

在 MATLAB Online 中打开

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)

请先登录，再进行评论。