MATLAB: How count NaN values and replace NaNs in a sequence with that number

Question

I have a vector [0 0 NaN 0 0 NaN NaN NaN 0 0 0 0 0 NaN] and I want [0 0 1 0 0 3 3 3 0 0 0 0 0 1]. Is it possible without a for cycle?

Answer 1

I don't think it's entirely possible to do it without a loop, but the loop can be limited to the number of sequences (3 steps in your example)

v = [0 0 NaN 0 0 NaN NaN NaN 0 0 0 0 0 NaN];
seqedges = find(diff([false, isnan(v), false]));
seqstarts = seqedges(1:2:end);
seqends = seqedges(2:2:end);
seqlengths = seqends - seqstarts;
for seq = 1:numel(seqstarts)
  v(seqstarts(seq):seqends(seq)-1) = seqlengths(seq);
end

edit: actually, it's possible without a loop:

v = [0 0 NaN 0 0 NaN NaN NaN 0 0 0 0 0 NaN];
nanlocs = isnan(v);
seqedges = find(diff([false, nanlocs, false]));
seqlengths = seqedges(2:2:end) - seqedges(1:2:end);
v(nanlocs) = repelem(seqlengths, seqlengths)