Replace for loop values saved as a vector using a condition

I'm trying to find a simple way to change values in a for loop that are 0 into 'NaN'. For example:

r = [1 9 0 0 1 2 5 16] and I want it to print [1 9 NaN NaN 1 2 5 16]

I was trying to for something like this:

for i = 1:size(r)     % r is 3 data samples with 100 values with the first 10 used for a baseline
  a = r(i,:);   
  thresh = mean(r(i,1:10))+ 2*std(r(i,1:10));
  start= find(a>thresh); %find where the numbers exceed the threshold
     if isempty(start)   %setting the traces without values above the threshold to zeros
     Rresults(i) = start(1);  %Saving the first value past the threshold in a vector
     start(start(1)<0) = 'NaN'
  end
end

I can't get the values to change using the method I have above. Any help or advice would be greatly appreciated.

Answer 1

[Star Strider]

Use ‘logical indexing’:

r = [1 9 0 0 1 2 5 16];
r(r==0) = NaN

r =
     1     9   NaN   NaN     1     2     5    16

This implicitly first creates a logical vector that is true for the 0 values, then replaces those values with NaN. See the documentation on Using Logicals in Array Indexing (link) for details.

[Austin Davies]

That worked! Thank you

[Star Strider]

My pleasure!

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