find similar numbers within a matrix
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Hi. I need to identify the position of a triplet of numbers (P) inside an array (M).
P = [-3.4970900e+01 -2.0289890e+02 -1.7948105e+02];
I am using the 'find' function but the numbers in P is very close to the respective numbers in M.
This does not determine the line of interest for me.
[r,c] = find(M(:,1) == P(1,1) & M(:,2) == P(1,2) & M(:,3) == P(1,3));
That is:
- P(1,1) is equal to or similar to M(?,1);
- P(1,2) is equal to or similar to M(?,2);
- P(1,3) is equal to or similar to M(?,3);
Instead, I determine the line of interest in this way:
[r,c] = find(M(:,1) == P(1,1));
p.s. The variation is only present after the decimal point.
Is there a way to identify within M the (very similar) values present in P? For example by considering a variation of +-0.01 in the numbers in M?
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Accepted Answer
Dyuman Joshi
on 11 Jan 2024
Edited: Dyuman Joshi
on 11 Jan 2024
arr = load('M.mat')
M = arr.M;
P = [-3.4970900e+01 -2.0289890e+02 -1.7948105e+02];
tol = 0.01;
%Rows that satisfy the condition for all column elements
idx = all(abs(M-P)<tol, 2)
%Get the output using the row indices
out = M(idx, :)
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More Answers (4)
John D'Errico
on 11 Jan 2024
Edited: John D'Errico
on 11 Jan 2024
Lots of good answers posted. I did not see this one.
load M.mat
size(M)
The array M has 61 rows.
P = [-3.4970900e+01 -2.0289890e+02 -1.7948105e+02];
And we want to find an element in M that is close to P.
help knnsearch
[idx,D] = knnsearch(M,P)
It tells us that row 16 of M is the closest one to P, and the distance between the two vectors is not exactly zero, but is very close.
format long g
M(idx,:)
P - M(idx,:)
So it misses only in the third element. If the distance is too arge to be acceptable, then D will tell you that. For example...
[idx,D] = knnsearch(M,[-100 -200 -300])
So that was a miss by a mile.
M(idx,:)
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VINAYAK LUHA
on 11 Jan 2024
Hi Alberto,
Try this
[r, ~] = find(abs(M(:,1) - P(1,1)) <= 0.01 & abs(M(:,2) - P(1,2)) <= 0.01 & abs(M(:,3) - P(1,3)) <= 0.01);
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Hassaan
on 11 Jan 2024
% Define the matrix M and the vector P
loadedArray = load('M.mat');
M = loadedArray.M;
P = [-3.49799e+01, -2.02899e+02, -1.794815e+02]; % example vector P
% Define the tolerance for similarity
tolerance = 0.01; % For example, 0.01 means we're allowing a difference of up to ±0.01
% Preallocate a logical array for row matches
row_matches = true(size(M, 1), 1);
% Loop through each element in P and update the row_matches array
for i = 1:length(P)
row_matches = row_matches & (abs(M(:, i) - P(i)) < tolerance);
end
% Find the row indices where all elements match P within the tolerance
matching_rows = find(row_matches);
% Display the matching row indices
disp('Matching row indices:');
disp(matching_rows);
---------------------------------------------------------------------------------------------------------------------------------------------------
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Steven Lord
on 11 Jan 2024
If you want to find a row of numbers that's close to (but perhaps not exactly equal to, due to roundoff error) another row of numbers, I would use the ismembertol function with the 'ByRows' option.
1 Comment
Dyuman Joshi
on 11 Jan 2024
Edited: Dyuman Joshi
on 16 Feb 2024
How similar is it to the code I've written? And if there is a significant difference, which code is better?
On the surface, it looks very similar -
arr = load('M.mat');
M = arr.M;
P = [-3.4970900e+01 -2.0289890e+02 -1.7948105e+02];
tol = 0.01;
idx = all(abs(M-P)<tol, 2)
out = M(idx, :)
IDX = ismembertol(M, P, tol, 'ByRows', 1)
OUT = M(IDX,:)
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