Find a row in a matrix in faster way
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Hi,
I have to compare two matrices: in detail, I have to find if each row of a matrix1 is contained in a matrix2. Then I have to store the corresponding positions in a vector.
The following is a trivial method and seems to be faster than ismember version.
if true
t1=tic;
for m=1:size(matrix1,1)
for l=1:size(matrix2,1)
if(sum(xor(matrix1(m,:), matrix2(l,:)))==0)
vector(m)=l;
end
end
end
toc(t1)
end
ismember version.
if true
t2=tic;
for m=1:size(matrix1,1)
index=ismember(matrix2,matrix1(m,:),'rows');
l=find(index);
vector(m)=l;
end
toc(t2)
end
Is there a way to speed up such computation? Thank
2 comentarios
Image Analyst
el 29 de Nov. de 2012
Are they integer or floating point? http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
Matt Fig
el 29 de Nov. de 2012
IA, the methods do not return the same results unless both matrices are binary....
Respuesta aceptada
Matt Fig
el 29 de Nov. de 2012
Editada: Matt Fig
el 29 de Nov. de 2012
Here is a faster method, in the script I use to compare:
M1 = rand(1000,8)>.5;
M2 = rand(1000,8)>.5;
tic % Method 1, use XOR
V1 = zeros(1,size(M1,1));
for m=1:size(M1,1)
for n=1:size(M2,1)
if(sum(xor(M1(m,:), M2(n,:)))==0)
V1(m)=n;
end
end
end
toc
tic % Method 2, use ISMEMBER
V2 = zeros(1,size(M1,1));
for m=1:size(M1,1)
index=ismember(M2,M1(m,:),'rows');
n = find(index,1,'last');
if ~isempty(n)
V2(m)=n;
end
end
toc
tic % Method 3, use BSXFUN
V3 = zeros(1,size(M1,1));
for m=1:size(M1,1)
index=all(bsxfun(@eq,M1(m,:),M2),2);
n = find(index,1,'last');
if ~isempty(n)
V3(m)=n;
end
end
toc
isequal(V1,V2,V3)
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