why knn classifier accuracy for multi class dataset is low?
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I have data set consist of 296 features for 37 class. The data set is ordered according to the classes. I trained and test the data using KNN classifier. However, the maximum accuracy that i have go is about 13.423%.
- why I got these low result I tried it on 296*21 features and 296*82 the result does not change much?
- Is this because I have 37 class, because most of the application i saw have about 3 classes?
- Is there any way to increase this accuracy or alternative evaluation way because the knn match result is success 100% ?
thank you
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Image Analyst
2018-2-25
编辑：Image Analyst
2018-2-25
Your classes, using the features/measurements you chose to use, are badly overlapped. If you were able to plot each data point in 296-space, you'd see that there is a lot of mixing of where the classes occur.
For example, in 1-space if you had 5 classes
class1 = rand(1,100); % Ranges from 0 to 1.0
class2 = 1.05 * rand(1,100); % Ranges from 0 to 1.05
class3 = 1.10 * rand(1,100); % Ranges from 0 to 1.10
class4 = 1.15 * rand(1,100); % Ranges from 0 to 1.15
class5 = 1.20 * rand(1,100); % Ranges from 0 to 1.20
If you plotted each class in a different color, you'd see that there is a tremendous amount of overlap in the 0 to 1 region because all classes have a value in that region.
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Eliza
2018-2-25
Image Analyst
2018-2-25
编辑：Image Analyst
2018-2-25
You might try deep learning, though I'd have my doubts even with that. It seems like you just chose the wrong (non-descriptive) measurements to use. Put effort into making sure the measurements you use are truly discriminative.
You might also try treebagger/random fortest.
Eliza
2018-2-25
Image Analyst
2018-2-25
With any method, your training set is assumed to be 100% accurate. Then you put through your test set. The only way to see if the test set was accurately predicted is to know the ground truth for that test set, otherwise all you have are predictions. So, with either NN or KNN if you got accuracy, you must have had ground truth (the known, correct classification).
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