Looking for a way faster than find?

Dear All,

I have an array A. I want to find out the index of those "1" entries in the array A.

For example, A = [1 2 5 1 3 2 8 10 1]. I want to find out the indecis of those "1" in A.

I used logical indexing to find the location but cannot get the indecis.

a = A == 1;

a = [1 0 0 1 0 0 0 0 1].

How can I find the indecis of nonzero in a?

Thanks.

Benson

Answer 1

[Joseph Cheng]

without doing some testing to actually test if its faster you can use the found 1's in a to only select a list of indexes

 A = [1 2 5 1 3 2 8 10 1];
 a = A==1

a = 1×9 logical array
   1   0   0   1   0   0   0   0   1

 inds = [1:numel(A)];
 inds(a)

ans = 1×3

1 4 9

[Benson Gou]

Hi, Joseph,

Thanks for your promt reply.

I compared the speed between find and your code. I found the following:

tic

a = A == 1;

inds = 1:numel(a);

c = inds(a)

toc

Elapsed time is 0.004136 seconds.

tic;

find(A==1);

toc

Elapsed time is 0.000365 seconds.

Using find is faster than the above code.

[Joseph Cheng]

but it did answer your i "I used logical indexing to find the location but cannot get the indecis... How can I find the indecis of nonzero in a?"