DZone
Web Dev Zone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
  • Refcardz
  • Trend Reports
  • Webinars
  • Zones
  • |
    • Agile
    • AI
    • Big Data
    • Cloud
    • Database
    • DevOps
    • Integration
    • IoT
    • Java
    • Microservices
    • Open Source
    • Performance
    • Security
    • Web Dev
DZone > Web Dev Zone > k - Nearest Neighbor Search

k - Nearest Neighbor Search

Giuseppe Vettigli user avatar by
Giuseppe Vettigli
·
Apr. 16, 12 · Web Dev Zone · Interview
Like (0)
Save
Tweet
5.55K Views

Join the DZone community and get the full member experience.

Join For Free
A k-nearest neighbor search identifies the top k nearest neighbors to a query. The problem is: given a dataset D of vectors in a d-dimensional space and a query point x in the same space, find the closest point in D to x. The following function performs a k-nearest neighbor search using the euclidean distance:
from numpy import random,argsort,sqrt
from pylab import plot,show

def knn_search(x, D, K):
 """ find K nearest neighbours of data among D """
 ndata = D.shape[1]
 K = K if K < ndata else ndata
 # euclidean distances from the other points
 sqd = sqrt(((D - x[:,:ndata])**2).sum(axis=0))
 idx = argsort(sqd) # sorting
 # return the indexes of K nearest neighbours
 return idx[:K]
The function computes the euclidean distance between every point of D and x then returns the indexes of the points for which the distance is smaller.
Now, we will test this function on a random bidimensional dataset:
# knn_search test
data = random.rand(2,200) # random dataset
x = random.rand(2,1) # query point

# performing the search
neig_idx = knn_search(x,data,10)

# plotting the data and the input point
plot(data[0,:],data[1,:],'ob',x[0,0],x[1,0],'or')
# highlighting the neighbours
plot(data[0,neig_idx],data[1,neig_idx],'o',
  markerfacecolor='None',markersize=15,markeredgewidth=1)
show()
The result is as follows:



















The red point is the query vector and the blue ones represent the data. The blue points surrounded by a black circle are the nearest neighbors.
Neighbors (app)

Published at DZone with permission of Giuseppe Vettigli, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

Popular on DZone

  • What SREs Can Learn From the Atlassian Nightmare Outage of 2022
  • Application Scalability — How To Do Efficient Scaling
  • An Overview of 3 Java Embedded Databases
  • Maven Tutorial: Nice and Easy [Video]

Comments

Web Dev Partner Resources

X

ABOUT US

  • About DZone
  • Send feedback
  • Careers
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • MVB Program
  • Become a Contributor
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 600 Park Offices Drive
  • Suite 300
  • Durham, NC 27709
  • support@dzone.com
  • +1 (919) 678-0300

Let's be friends:

DZone.com is powered by 

AnswerHub logo