I have a large vector, I would like to find a set of data which is a subset of the large vector.

Any algorithm I can use to find the set of data?

[madhan ravi]

doc ismember

[Geoff Hayes]

Yun - please clarify what you mean by I would like to find a set of data which is a subset of the large vector. Do you mean that you want to create subsets of the larger vector? Or, if you have an array of elements, do you want to see if it is a subset of the large vector? Please illustrate with a small example.

[Yun Zhang]

Hi Geoff,

Thanks for the message. I did not explain my problem clearly.

I have a large vector and a small vector. The small vector is a subset of the large vector. for instance, the large vector is A=[1 2 3 4 5 6 7 8]. The smaller vector is B = [5 6].

I am looking for an algorithm to find the index of A which value matches B. For the above example, the index should be 6.

I hope it is clear now.

Thanks,

Yun

[madhan ravi]

what about 5?

[Yun Zhang]

Sorry, it is a typo. It should be 5

[madhan ravi]

;-) shouldn’t it be 5&6?

[John D'Errico]

No reason to add an answer for no reason. Moved to acomment:

"I meant the first index should be 5"

Answer 1

[madhan ravi]

[lo,ii]=ismember(B,A);
index = ii(lo)

Answer 2

[John D'Errico]

ismember is exactly the tool to solve your problem.

A = [1 3 5 7 9 8 6 4 2];
B = [5 6];

[LIA,LOCB] = ismember(A,B)
LIA =
  1×9 logical array
   0   0   1   0   0   0   1   0   0
LOCB =
     0     0     1     0     0     0     2     0     0

So we see that elements 3 and 7 of A are in B.

find(LIA)
ans =
     3     7

And that seems to be what you are asking to learn.

[Yun Zhang]

ismember is not the right tool. The data I searched has to be in the right order. for instance, B=[5 6] and A=[ 1 3 5 7 6 5 6]. The search result has to be index 6 and 7.

[madhan ravi]

[r,c]=find(A.'==B);
G=findgroups(c);
index = splitapply(@max,r,G).'