How can a logical vector be converted to a numeric vector in which the values represent the number of zeros between ones?

I am searching for a simple way to convert a logical vector, to a vector in which the values represent the total number scalars between ones, and including the first 1 in the list. Essentially converting x to y where:

x = [1;1;1;0;0;1;0;1];
y = [1;1;3;3;3;2;2;1];

Any suggestions? Thanks!

RTT

[Walter Roberson]

Please explain further how you get that y from that x ?

Answer 1

[Ahmet Cecen]

Something along the lines of:

x = [1;1;1;0;0;1;0;1];
inds = find(x);
diffs = [inds(2:end);0]-inds;
diffs(end) = 1;  
y = repelem(diffs, diffs); % By Guillaume

[Guillaume]

I don't understand the logic of the algorithm.Why is the first element of diffs is removed and why is the last element set to 1? However, I can say that the loop is not needed and can be replaced by:

y = repelem(diffs, diffs);

[Ahmet Cecen]

Wow! What a nice function that I had never heard of. Super useful.

The example in the question is basically using the 1's in the matrix as nodes, and the 0's between 1's as the edge weights.

The algorithm is first finding where the ones are, then finds the distance between them ([inds(2:end);0] is aligning the next index with current for the subtraction.). It is a similar effect to circshift, but I didn't want to confuse the reader with periodicity when it is not used here. Last element is set to 1 simply assuming the list ends with a 1, as it is unclear from the question how a list ending with a 0 would be treated.

Answer 2

[Robert]

Very elegant solution, thank you!

Cheers