Find a row in a matrix in faster way
显示 更早的评论
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 个评论
Image Analyst
2012-11-29
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
2012-11-29
IA, the methods do not return the same results unless both matrices are binary....
采纳的回答
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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