Is there a function like "ismember" but more efficient?

Question

For example,A is the number set.b is elements.

I want to test whether the number in b is the element of the set A.

I know the matlab function "ismember" could do this ,but it's not fast enough when I use it one million times.

b=[1,2,9,100];
A=[1,2,3,4,5,6,7,8,9];
tic;for ii=1:1e6,ismember(b,A);end;toc
Elapsed time is 45.714583 seconds.

I want to return [1,1,1,0],because 1,2,9 are in the set A,while 100 is not.

Do you know some functions like ismember or some ways more efficient than "ismember"?

Answer 1

You can use the mex version, i.e. ismemberoneoutput. The mex version is much faster.

b=[1,2,9,100];
A=[1,2,3,4,5,6,7,8,9];
tic;for ii=1:1e5,ismember(b,A);end;toc
%Elapsed time is 9.537219 seconds. On my pc

% A must be sorted!!! In this example it is already sorted,
% so no need for this here.
tic;for ii=1:1e5,builtin('_ismemberoneoutput',b,A);end;toc
%Elapsed time is 0.376556 seconds. On my pc