Find similar rows but not equal at the same matrix

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Libros Construccion
编辑： Libros Construccion 2017-5-17
Hi,
I have a mx3 matrix and need to find which rows are very close one another. For example
[a b c
d e f
a b c+1e-8
d e f
g h i
g h+1e-5 i
];
ans= [1,3 ; 5,6] %ignoring the rows that hasn't at least one similar. It's something like a min_tol to accept and an max_tol to reject
I've been thinking about tolerances with find(), unique, uniquetol(), intersection(?) or perform some calculations to get it, but i have only figure it out in ways that enlarge too much my data. Any guide Thanks!
  2 个评论
Stephen23
Stephen23 2017-5-17
Why are rows 2 and 4 not listed in your example output?
Libros Construccion
Libros Construccion 2017-5-17
Because i don't want equals rows, just similar ones. unique() clear one of them, but i get row 2 outputted when i try it.

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采纳的回答

Libros Construccion
编辑：Libros Construccion 2017-5-17
Hey, thanks!. I'll try to follow your guides. Maybe i can combine them with this, which is getting me where i want.
A=[1 2 3; 1+1e-5 2 3; 1 2 3;1+1e-8 2 3];
simA=find(ismember(A,uniquetol(A,1e-6,'ByRows',true),'rows')==0);
ans=4

更多回答（1 个）

Jan
Jan 2017-5-17
编辑：Jan 2017-5-17
pdist replies the pairwise distances between the rows. Then you can filter out the values:
D = pdist(Data);
Match = (D ~= 0 & D < 1e-4);
Without the Statistics Toolbox you can calculate the distance matrix manually also. If the input is not huge, a loop might be useful also, because you can remove the unwanted element directly:
n = 1000;
data = rand(n, 3);
check = true(1, n);
result = zeros(n, 2); % Pre-allocate
iResult = 0;
limit = 1e-4 ^ 2; % Squared limit to avoid SQRT
for k = 1:n
if check(k) % Not included before (is this wanted?!)
dist = sum(data(k, :) - data(k+1:n, :)).^2, 2);
match = find(dist > 0 & dist < 1e-2);
...
end
end
Sorry, I cannot finish this code, because I found some open questions. What should happen for:
a b c
d e f
a b c+1e-4
a+1e-4 b c
Or if the limit is 1e-4, what about this:
a b c
a b c+1e-4
a b c+2e-4
What is the wanted result?
Why does the output have less columns than the input?

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