How to efficiently find index of matrix elements in another matrix
Altair EmployeeHello,
I have a matrix A of size 350000X1 and i want to find index of A in matrix B of size 900000 X 1. I used "Intersect" as below and it takes ~5 mins to get the result. Is there an efficient way to achieve this any faster?
[x,y,z] = intersect(A,B);
thanks,
Manoj kandukuri
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Altair EmployeeThank you Roberta,
I need "y" & "z" (which consists of index of each element of A in matrix 
. I need to parse these index to readcae command as requests.
thanks,
manoj kandukuri
What about adding these 2 commands after what I already suggested?
[bool,y2] = ismember(x2,A);
[bool,z2] = ismember(x2,B);
Results are the same (y is the original approach you shared and y2 is the new one):
It is still more than 2 times faster:
Elapsed time is 8.715 seconds.
Elapsed time is 3.456 seconds.
Regards,
Roberta
PS: I wrote x2 in my latest commands, but I guess it should have been x3, to be aligned with my previous comment!
Roberta
@Manoj Kandukuri,
Are you willing to store only x results or do you also need y and z? Because in case you need only x, this solution is much faster:
x3 = unique(A(ismember(A,B)))
As a comparison, if you run these commands, which I created to replicate your scenario:
It is around 4 times faster with the second approach:
Elapsed time is 5.662 seconds.
Elapsed time is 1.344 seconds.
Regards,
Roberta