complex logical indexing?

לק"י

Hello!

lets assume I want to logically index a vector, or create a new vector that will hold the results of these logical indexing and it's complex as follow:

A - Vector that contain the index (1, 2, 3, 4, etc.) of areas (not the areas themeself, like 1.243, 2, 453.345 etc).

B - Cell array that contains numerical data in each cell (for example, {1, 25, 33, 15}) of indexes of another vector C.

C - Vector that contain 2 columns (x and y points) of a vertices, the first C(:,1) the X points of the vertices, C(:,2) the Y points of the vertices.

D - Vector that contain 2 columns (x and y points) of a vertical line, the first D(:,1) the X points of the vertical line, D(:,2) the Y points of the vertical line.

E - Vector that contain 2 columns (x and y points) of a horizontal line, the first E(:,1) the X points of the horizontal line, E(:,2) the Y points of the horizontal line.

I wish to find all the coresponding indexes in A that:

corresponding cell index in cell array B won't contain the number '1'. (so if B(1) = {1,2,25,33,56,123} it will give back a 0)

AND

areas correspond to the index of A and cross one of the two lines C and D (vertical or horizontal).

I know the conditios that do it are:

ismember(1, B{j})==0 && (isempty(polyxpoly(D(:,1),D(:,2),C(B{j},1),C(B{j},2)))==0 || isempty(polyxpoly(E(:,1),E(:,2),C(B{j},1),C(B{j},2)))==0)

I can do it with for loop such as:

for j=1
    if ismember(1, B{j})==0 && (isempty(polyxpoly(D(:,1),D(:,2),C(B{j},1),C(B{j},2)))==0 || isempty(polyxpoly(E(:,1),E(:,2),C(B{j},1),C(B{j},2)))==0)
end

But I would be much faster and easier to somehow skip the loop.

Thanks (Jan?)!

Amit.

[Jan]

I try to onvert the text description to explicit code:

A = 1:33;
B = {1, 25, 33, 15};
C = rand(33, 2);
D = rand(33, 2);
E = rand(33, 2);

"corresponding cell index in cell array B won't contain the number '1'. (so if c(1) = {1,2,25,33,56,123} it will give back a 0)" - What is c(1) = {1,2,25,33,56,123} ? A lower case "c" did not appear before.

Anyway, to exclude cells containing a 1:

any([c{:}] == 1)

"areas correspond to the index of A and cross one of the two lines C and D (vertical or horizontal)." - I have only a faint idea of what this means.

I'd expect B{j} ~= 1 to be much faster than ismember(1, B{j})==0 .

I suggest, you improve my guessed example code. Then we get a step nearer to a solution.

Don't let my numerous questions for clarification confuse you. Finding a completely clear formulation of a question is almost the full way to get a solution. Of course this is omplicated. Otherwise the problem would be trivial :-)

[Amit Ifrach]

לק"י

Hi Jan, thanks again!

I think I need to correct the B cell array, for it consists of many cells, so:

A = 1:33;

B = {1, 25, 33, 15}, {3, 34, 625, 7 878} , {85, 14, 2, 7, 100} , {4, 32, 6} etc.;

C = rand(33, 2);

D = rand(33, 2);

E = rand(33, 2);

about the lower case c:

""corresponding cell index in cell array B won't contain the number '1'. (so if c(1) = {1,2,25,33,56,123} it will give back a 0)" - What is c(1) = {1,2,25,33,56,123} ? A lower case "c" did not appear before."

I edited several times this post so I missed this. it should be B(1). I edited to be correct it in the main post up there.

What I actually do is to plot an X over a photo, proir to a plot of polygons of areas like so:

First, a red cross is plotted on the image that contain points -

After that the points are being 'tranlated' to polygons of areas of these points with voronoi command, like this -

Then I ask which of these plotted polygons are being 'touched' or 'crossed' by the red cross I plotted.

As you can see from the image, I can get the answer. I just want it to be much quicker. and generlize it to other matrices for future work.

Is that clear enough?

Just for being accurate enough, I will add an example vectors from my code in a .mat file, please be aware that Cexample in the file is C here, I just saved with another name to evade overide my C variable.

Thanks alot :)

Amit.

[Bruno Luong]

@Amit Ifrach "areas correspond to the index of A and cross one of the two lines C and D (vertical or horizontal)"

Using polyxpoly to check a Voronoi cell crossing vertical and horizontal is overkill, it is enough to check the x or y coordinates are in both sides of the line vertical or horizontal coordinates.

Answer 1

[Sarthak]

Hi,

You can use logical indexing to achieve this without a for loop. Please refer to the following code for better understanding:

% Find indices where B does not contain 1 
idx = cellfun(@(x) ~ismember(1,x), B); 
% Find indices where areas correspond to the index of A and cross one of the two lines C and D (vertical or horizontal) 
idx_cross = any(polyxpoly(D(:,1),D(:,2),C(A,1),C(A,2)),2) | any(polyxpoly(E(:,1),E(:,2),C(A,1),C(A,2)),2); 
% Combine the two conditions using logical AND (&) operator to get the final index vector 
idx_final = idx & idx_cross; 
% Use the final index vector to get the corresponding indices in A 
result = A(idx_final); 

[Amit Ifrach]

לק"י

Thanks!