Convert Logical into Sequential Index Vector

Hello,

I am looking for a simple way to convert a logical vector in a sequential vector of doubles whose values are the indices of true in the logical vector. For example, let's say x is a 1x8 logical vector:

x = [0 1 0 0 1 1 1 0]

The result I am looking for would be y:

y = [2 5 6 7]

I know this can be done with a for loop, but was curious if there is a clever one-liner.

Thank you.

Answer 1

[Star Strider]

Us e the find function:

x = [0 1 0 0 1 1 1 0];
y = find(x)

y =
     2     5     6     7

[Gabor]

Hi,

What if we want to do the exact opposite?

We have y = [2 5 6 7] and we want to create x = [0 1 0 0 1 1 1] without loop?

x(ismember(1:max(y),y))=true

than we get our logical vector array without loop from a list of indexes

x =

1×7 logical array

0 1 0 0 1 1 1

I hope it helps someone, it took me sometime to figure this out.

Keywords: create logical vector from array of indexes, from index array, from idx, from vector of indexes.

[Star Strider]

That can be significantly simplified:

y = [2 5 6 7]

y = 1×4

2 5 6 7

x(y) = true

x = 1×7 logical array
   0   1   0   0   1   1   1

If ‘x’ is already longer than 7 elements (for example to reconstitute the original 8-element vector):

x = zeros(1,8)

x = 1×8

0 0 0 0 0 0 0 0

x(y) = true

x = 1×8

0 1 0 0 1 1 1 0

.