Search for an array in a matrix to store indices of the matrix where its located.

Lets say, I have an array. a= [] of nx1 entries. where n is the no. of entries. I have another matrix, B = (m,m) where m is the no. of entries in the matrix.

I want to apply to get only the row indices of the matrix B, where the entries match. This check should be done column-wise in B. Simple eg. a = [ 100 200 300 400 500] B= [7 100; 8 200; 9 300;10 400;11 500;12 6;] This should give an output [1,2,3,4,5] since the indices in B of the second column match.

I tried ismember, find, interesect without much success.

Thanks for the help, in advance !!

[Guillaume]

What should the output be for:

 a = [ 100 200 300 400 500] 
 B = [ 7    100  100
       200  200  400
       100  300  5
       100  400  7
       6    7    8]

It could either be

[1 2 3 4]
[1 1 2 2 2 3 3 4 4]
[2 3 4 1 2 3 4 1 2]

[Guillaume]

Chaitanya Sanghavi's comment moved here:

Clarifying the question a bit more :

1. All the entries of a = [100 200 300 400 500] will be in the same column as B. 2. In case this is array is present in different columns. chose the smallest row indices of B.

Answer 1

[Guillaume]

I'm not entirely sure what it is you're asking. From your example, it looks like you want to know which rows of B have an element in a, so it wouldn't be indices as per your title. Also what if a row of B has more than one column present in a, should that row be present several time in the output?

With your example inputs, the following give the answer you've shown:

a = [ 100 200 300 400 500]
B = [7 100; 8 200; 9 300;10 400;11 500;12 6;]
[rows, ~] = find(ismember(B, a))  %you have to request two outputs from find to get the rows

[Guillaume]

You've accepted my answer but I'm not sure it's what you want. Particularly, with regards to your clarification, it does not check if all the entries of a are present, and if an entry is present in multiple rows/columns it will return that location multiple time.

I'm still not 100% what it is you exactly want.