I'm trying to simulate 3 nearest neighbour classification without using the builtin matlab functions. I was able to 1 nearest neigbhor however i am unable to extend it to more

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Mujeeb Ul Hassan 2022-4-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1695835-i-m-trying-to-simulate-3-nearest-neighbour-classification-without-using-the-builtin-matlab-functions

评论： Mujeeb Ul Hassan 2022-4-14

%% code for 1 nearest neighbor classification
total_num_test_cases = num_test_cases * 5; %75
total_num_train_cases = num_train_cases * 5; %175
% Create a vector to store assigned labels
inferredLabels = zeros(1, total_num_test_cases);
% This loop cycles through each unlabelled item:
for unlabelledCaseIdx = 1:total_num_test_cases
    unlabelledCase = testingSet(unlabelledCaseIdx, :);
    
    % As any distance is shorter than infinity
    shortestDistance = inf;
    shortestDistanceLabel = 0; % Assign a temporary label
    
    % This loop cycles through each labelled item:
    for labelledCaseIdx = 1:total_num_train_cases
        labelledCase = trainingSet(labelledCaseIdx, :);
        
        % Calculate the Euclidean distance:
        currentDist = euc(unlabelledCase, labelledCase);
        
        % Check the distance
        if currentDist < shortestDistance
            shortestDistance = currentDist;
            shortestDistanceLabel = trainingTarget(labelledCaseIdx);
        end
    end % inner loop
    
    % Assign the found label to the vector of inferred labels:
    inferredLabels(unlabelledCaseIdx) = shortestDistanceLabel
end % outer loop

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Answer 1

Image Analyst 2022-4-13

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https://ww2.mathworks.cn/matlabcentral/answers/1695835-i-m-trying-to-simulate-3-nearest-neighbour-classification-without-using-the-builtin-matlab-functions#answer_942135

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Attach your test and training sets of data. You can get the distances of a point to all other points in one line of code. Then sort it in ascending order.

distances = sqrt((x - allX) .^ 2 + (y - allY) .^ 2);
[sortedDistances, sortOrder] = sort(distances)
indexesOfClosest3 = sortOrder(1:3)

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Image Analyst 2022-4-14

在 MATLAB Online 中打开

OK so I interpret that as you don't want to try my solution yourself and just want me to do it for you. Here it is:

numPoints = 30;
allX = 100 * rand(1, numPoints);
allY = 100 * rand(1, numPoints);
plot(allX, allY, 'b.', 'MarkerSize', 40);
grid on;
hold on;
drawnow;
indexesOfClosest3 = zeros(numPoints, 3);
for k = 1 : numPoints
    x = allX(k);
    y = allY(k);
    distances = sqrt((x - allX) .^ 2 + (y - allY) .^ 2);
    [sortedDistances, sortOrder] = sort(distances);
    indexesOfClosest3(k, :) = sortOrder(2:4); % Don't include the first distance which is zero (the distance of the point to itself).
    % Plot lines to them
    for k3 = 1 : 3
        x3 = allX(indexesOfClosest3(k, k3));
        y3 = allY(indexesOfClosest3(k, k3));
        line([x, x3], [y, y3], 'Color', 'r', 'LineWidth', 2)
    end
end