How to merge adjacent NaN values into single NaN value in a vector?

I have [1 2 3 NaN NaN 0 1 2 NaN 9 8 7 6 NaN NaN NaN 1 1] anf I want [1 2 3 NaN 0 1 2 NaN 9 8 7 6 NaN 1 1] without a for cycle. Are there any trick to do this?

[Stephen23]

@Mr M: please remember to accept answers or provide feedback on your earlier questions:

https://www.mathworks.com/matlabcentral/answers/408164-how-to-interpolate-at-nan-values

https://www.mathworks.com/matlabcentral/answers/408162-how-count-nan-values-and-replace-nans-in-a-sequence-with-that-number

Answer 1

[Stephen23]

No loops required, no tricks required, just basic MATLAB indexing:

old = [1 2 3 NaN NaN 0 1 2 NaN 9 8 7 6 NaN NaN NaN 1 1];
idx = ~isnan(old);
new = old(idx | [true,idx(1:end-1)]);

[Andrei Bobrov]

+1! Super!

[Mr M.]

Sorry, but this is wrong when old vector starts with NaN values!

[Stephen23]

@Mr M.: you are right. It is easy to fix, just exchange the false for true:

>> old = [NaN,NaN,NaN,1,2,3,NaN,NaN,0,1,2,NaN,9,8,7,6,NaN,NaN,NaN]
old =
   NaN   NaN   NaN     1     2     3   NaN   NaN     0     1     2   NaN     9     8     7     6   NaN   NaN   NaN
>> idx = ~isnan(old);
>> new = old(idx | [true,idx(1:end-1)])
new =
   NaN     1     2     3   NaN     0     1     2   NaN     9     8     7     6   NaN

Answer 2

[Andrei Bobrov]

a = [1 2 3 NaN NaN 0 1 2 NaN 9 8 7 6 NaN NaN NaN 1 1];
lo = ~isnan(a);
lo(strfind(lo,[0 1])) = true;
out = a(lo);