K-Nearest Neighbors is one of the most basic yet essential classification algorithms in Machine Learning. It belongs to the supervised learning domain and finds intense application in pattern recognition, data mining and intrusion detection.
It is widely disposable in real-life scenarios since it is non-parametric, meaning, it does not make any underlying assumptions about the distribution of data (as opposed to other algorithms such as GMM, which assume a Gaussian distribution of the given data).
We are given some prior data (also called training data), which classifies coordinates into groups identified by an attribute.
As an example, consider the following table of data points containing two features:
Now, given another set of data points (also called testing data), allocate these points a group by analyzing the training set. Note that the unclassified points are marked as ‘White’.
If we plot these points on a graph, we may be able to locate some clusters, or groups. Now, given an unclassified point, we can assign it to a group by observing what group its nearest neighbours belong to. This means, a point close to a cluster of points classified as ‘Red’ has a higher probability of getting classified as ‘Red’.
Intuitively, we can see that the first point (2.5, 7) should be classified as ‘Green’ and the second point (5.5, 4.5) should be classified as ‘Red’.
Let m be the number of training data samples. Let p be an unknown point.
- Store the training samples in an array of data points arr. This means each element of this array represents a tuple (x, y).
for i=0 to m: Calculate Euclidean distance d(arr[i], p).
- Make set S of K smallest distances obtained. Each of these distances correspond to an already classified data point.
- Return the majority label among S.
K can be kept as an odd number so that we can calculate a clear majority in the case where only two groups are possible (e.g. Red/Blue). With increasing K, we get smoother, more defined boundaries across different classifications. Also, the accuracy of the above classifier increases as we increase the number of data points in the training set.
Assume 0 and 1 as the two classifiers (groups).
The value classified to unknown point is 0.
This article is contributed by Anannya Uberoi. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
- Text extraction from image using LSB based steganography
- Microsoft TechSetGo Summer Internship Interview Experience
- ML | Implement Face recognition using k-NN with scikit-learn
- Number of ways to make binary string of length N such that 0s always occur together in groups of size K
- Count integers in a range which are divisible by their euler totient value
- Count maximum elements of an array whose absolute difference does not exceed K
- Count how many times the given digital clock shows identical digits
- Count pairs in array whose sum is divisible by K
- Check if the given string is K-periodic
- How to use Google Colaboratory for Video Processing
- Find the modified array after performing k operations of given type
- Sum of (maximum element - minimum element) for all the subsets of an array.
- Number of ways to remove elements to maximize arithmetic mean
- Bag of words (BoW) model in NLP
Improved By : NIRBHAYKUMAR1