How to assign value in an array depending on the index stated in another array

Hi all,

After performing some processing, now the variable 'a' contains [2 5 9].

Let say i have another variable 'b', variable 'b' is pre-initialized to be zero depending on a length of input, let say 10. b = [0 0 0 0 0 0 0 0 0 0];

What I want is, the elements that are stated in variable 'a' should be set ONE in variable 'b'. b= [0 1 0 0 1 0 0 0 1 0]

How could I do this in Matlab? Appreciate any idea, thanks

Answer 1

[Mischa Kim]

Use

b(a) = 1

[want2know]

Thanks so much... What is wrong if I got this error when using b(a)=1?

I did make sure variable 'a' contains only positive integers.

Subscript indices must either be real positive integers or logicals.

Answer 2

[Jos (10584)]

Welcome to the world of indexing!

Your problem:

a = [2 5 9]
b = [0 0 0 0 0 0 0 0 0 0];
b(a) = 1

Other interesting indexing things:

a = [1 3 7]
b = [0 0 0 ];
b(a) = 1 % automatic expansion of b

a = [2 2 2 2]
b = [0 0 0 0]
b(a) = 1 % no adding up ...

[want2know]

Thanks so much... What is wrong if I got this error when using b(a)=1?

I did make sure variable 'a' contains only positive integers.

Subscript indices must either be real positive integers or logicals.

[Jos (10584)]

This means that values of a are not real positive integers. Think about this, e.g. when a = 2.13;

What should the 2.13th element of b be?

You can often use round to obtain meaningful indices ...

[want2know]

Thanks. I did make sure variable 'a' contains only positive integers.

'a' can only be positive integers, I confirm and have checked.

I have also added this line "a=round(a); b(a)=1;" still I got the same error...

[Image Analyst]

What does all this show

a
class(a)
whos a
min(a(:))
max(a(:))