# Convert Logical into Sequential Index Vector

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John R. on 2 Feb 2016
Commented: Star Strider on 25 Jun 2021
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.

Star Strider on 2 Feb 2016
Us e the find function:
x = [0 1 0 0 1 1 1 0];
y = find(x)
y =
2 5 6 7

Gabor on 25 Jun 2021
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 on 25 Jun 2021
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
.

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