WHY LOGICAL INDEXING REDUCE TOTAL ROW COUNT

Dear MATLAB,

I notice strange thing happen when use logical indexing. Specifically, the number of row is reduced.

Is this a bug? I am using MATLAB2017a

Thanks in advance for any insight.

The code are as follow

load('help_ismember'); % attached together with this question
NonNanPVT_Logic=ismember(Validtn_Loc,Validtn_Loc_MIA); % 37 row
KSS_valid_WithNan(NonNanPVT_Logic==0)=ev.KSS_valid(NonNanPVT_Logic==0); %Output reduced to 36

[Stephen23]

"Is this a bug?"

Not really, This behavior is easy to demonstrate:

>> X = [true,true,false,false];
>> A(X) = 3
A =
   3   3

What size would you expect A to be?

[polo sepian]

Yes, you are right, it is more about how I position the variable.

Really appreciate for your time.

Answer 1

[Steven Lord]

I suspect KSS_valid_WithNan didn't exist before that last line and that the last element of NonNanPVT_Logic == 0 was false.

x = (1:10).'
y = mod(x, 2) == 1 % Select odd numbers
z(y) = x(y)

The elements in the (non-existent) vector z to which values were assigned were 1, 3, 5, 7, and 9. Even though y has 10 elements, the last true value was in position 9.

If you want to control the size (and shape) of the vector z, preallocate it before assigning into it. For instance, if you want it to be exactly the same size and shape as x call zeros, ones, etc. passing the size(x) as the size of the array to create.

x = (1:10).'
y = mod(x, 2) == 1 % Select odd numbers
z2 = zeros(size(x));
z2(y) = x(y)

[polo sepian]

Thanks for the solution.

Appreciate it