Index in position 2 exceeds array bounds (must not exceed 1)?

Why does the following for loop produce the error "Index in position 2 exceeds array bounds (must not exceed 1)"?

data matrix (1000x4)

x = data(:,2); 
y = data(:,3); 
tr = data(:,4); 
xt = x((tr)==1); 
yt = y((tr)==1); 

for i = 1:size(x) 
     for j = 1:size(xt) 
         if  sqrt((x(1,i)-xt(1,j))+(y(1,i)-yt(1,j)))< 5
             fprintf ('Pass')
         end 
     end
 end

Answer 1

[Walter Roberson]

size(x) returns a vector of values -- size() with a single parameter always returns two values.

When you use a vector of values as the boundary in a colon operation, 1:size(x) for example, then it will use the first element as the bound. That might or might not be what you want.

x = data(:,2); 

That is going to be a column vector.

xt = x((tr)==1); 

When you do logical indexing on a row vector, you get out a row vector. When you do logical indexing on any other orientation (column vector, 2D array, etc.) then you get out a column vector. x is a column vector, so logical indexing on it is going to return a column vector.

         if  sqrt((x(1,i)-xt(1,j))+(y(1,i)-yt(1,j)))< 5

You are trying to index the column vectors x and xt as if they are row vectors.

You have the same issue with respect to y and yt.