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

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Chaitanya Sanghavi
Chaitanya Sanghavi 2017-12-21
评论： Guillaume 2017-12-21
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 !!
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Guillaume
Guillaume 2017-12-21
编辑：Guillaume 2017-12-21
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
Guillaume 2017-12-21
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.

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Guillaume
Guillaume 2017-12-21
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
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Guillaume
Guillaume 2017-12-21
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.

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