How to find the index of a randomly chosen element of an array

Would anyone suggest me the code of finding out the index of a randomly selected element of an array or matrix?

For example, after randomly selecting an element from 'a', I want to find out the index number of the chosen element. This index number should be a variable as each time i randomly select an element, the corresponding index number of the selected element may change.

a = [4 5 10 15 20];

Answer 1

[Ameer Hamza]

Try this

idx = find(a==random_element)

[feit feit]

Is the syntax same for matrix? How I can find the index of an element of a matrix if the element value is known?

[James Tursa]

[row,col] = find(a==random_element)

[feit feit]

Hi, the above code displays all [row,col] combination with the same value.

a = [ 1 3 4; 1 4 5; 2 1 6]

For example, , if a == 1, then the above code is displaying -

row =

1

2

3

col=

1

1

2

How can I see a particular element index Not all indexes having the same value? For example, I just meant to use [3,2].

Thank you

[Ameer Hamza]

What is the criteria to decide which combination you want? Do you always wants the last combination?

[feit feit]

Row number is the criteria. I will have a row number (which is also a variable) and i only need the combination corresponding to that particular row number.

[Ameer Hamza]

You can just apply find() to that row

a = [ 1 3 4; 1 4 5; 2 1 6];
row_num = 3;
random_element = 1;
col_num = find(a(row_num,:)==random_element)

Answer 2

[Steven Lord]

Start off generating the index and use it to extract the element.

a = [4 8 15 16 23 42];
I = randi(numel(a));
fprintf("Element %d of a is %d\n", I, a(I))

Element 5 of a is 23

[feit feit]

Very helpful answer. Thank you!