Trying to find row number in a large matrix

Hi all, I am writing a code that need to be able to find the particular row number in a large nx3 matrix (where n will eventually be >100000). I created a line of code to accomplish this task, but above n=20000 it does not work. Each row is unique (the matrix will never repeat a line).

row_num = max(find(ismember(pts,[X Y Z],'rows'))        %[X Y Z] is defined with a loop

Does anyone know of a way to run this where it will function at a higher n value.

edit: pts is the name of the nx3 matrix

edit: ismember is causing the problem (it is acting like it has a size limit)

[Tommy]

I don't have any problem with the following code, although I realize there may be more differences between my code and yours than meet the eye:

pts = rand(1000000,3);
target = randi(1000000);
row = pts(target,:);
row_num = find(ismember(pts,row,'rows'),1,'last');
assert(row_num == target)

Is it possible you should be using ismembertol?

[per isakson]

I fail to reproduce the propblem you report on my R2018b/Win10!

"(it is acting like it has a size limit)" what exactly does that mean? Full error meassage please!

[Will Schneider]

I believe that my issue was caused by user error. Sorry.

Answer 1

[per isakson]

Your one-liner is missing a closing parentheses and Matlab proposes an improvement

rigth-clicking "find" opens a context menu and Matlab offers to do the change

Add the ")" and your code works fine on R2018b/Win10

%%
pts = randi( 1e6, 1e6,3 );  % whole numbers
%%
x = pts( 5e5, 1 );
y = pts( 5e5, 2 );
z = pts( 5e5, 3 );
row_num = find( ismember( pts, [x,y,z], 'rows' ), 1,'last' )
%%
z = pts( 5e5, 3 ) + 17;
row_num = find( ismember( pts, [x,y,z], 'rows' ), 1,'last' )
%%
z = pts( 5e5, 3 );
row_num = max(find(ismember(pts,[x,y,z],'rows')) )

outputs

row_num =
      500000
row_num =
  0×1 empty double column vector
row_num =
      500000  
>>