Compare for uniqueness between 2 very large matrices

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Koren Murphy
Koren Murphy 2021-1-13
编辑： Adam Danz 2021-1-15
I have two matrices of the same size - 95 x 100,000.
They are in different orders but I would like to compare if columns in one matrix are repeated elsewhere in the other matrix - or if the 2 matrices are completely unique?
  2 个评论
Iuliu Ardelean
Iuliu Ardelean 2021-1-13
https://uk.mathworks.com/help/matlab/ref/double.ismember.html
You can use Lia = ismember(A,B,'rows'), which returns a vector of ones and zeros of length(A), representing those rows of A which are members of B.
You will need to transpose your matrices though.
Jan
Jan 2021-1-14
I do not understand this sentence: "I want to know if the columns are completely unique - even if the same rows are filled in each they could have different values."
ismember(x,y,'rows') searches for equal rows in both matrices. This is exactly, what "if columns in one matrix are repeated elsewhere in the other matrix" means, isn't it?

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回答（1 个）

Adam Danz
Adam Danz 2021-1-13
编辑：Adam Danz 2021-1-13
To determine if two arrays are 100% identical, use isequal or isequaln to ignore NaN values.
To determine if columns in matrix A are found in matrix B,
% create demo data
rng('default')
A = randi(3,3,20);
B = randi(4,3,20);
for i = 1:size(A,2)
isInB(i) = ismember(A(:,i)', B','rows');
end
isInB is a 1xn logical vector for n columns of A where isInB(i) indicates whether column i of A is found in B.
To find the column numbers in B that match each column number in A
isMatchInB = false(size(A,2),size(B,2));
for i = 1:size(A,2)
isMatchInB(i,:) = arrayfun(@(j)isequaln(A(:,i),B(:,j)),1:size(B,2));
end
isInB = any(isMatchInB,2);
isInB is a 1xn logical vector for n columns of A where isInB(i) indicates whether column i of A is found in B.
isMatchInB is an ixj logical vector where isMatchInB(i,j) indicates where colum i of A matches column j of B.
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Adam Danz
Adam Danz 2021-1-14
You could try storing the subscript indicies instead,
c = cell(1,size(A,2));
for i = 1:size(A,2)
c{i} = find(arrayfun(@(j)isequaln(A(:,i),B(:,j)),1:size(B,2)));
end
Bruno Luong
Bruno Luong 2021-1-14
编辑：Bruno Luong 2021-1-14
Or using sparse matrix
isMatchInB = sparse([],[],false(0),size(A,2),size(B,2));

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