k-Nearest Neighbors
Classifying by closest examples.
k-Nearest Neighbors is a free Data Science Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Data Science Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Judged by Your Neighbors
k-Nearest Neighbors classifies a point by looking at the examples closest to it. Birds of a feather end up in the same class. 🐦
No Real Training
kNN is a lazy learner: it just memorizes the data. The real work happens later, when a new point asks for a label.
Measure the Distance
To find who is near, the model computes a distance to every training point, most often plain straight-line distance.
Take a Vote
The closest k neighbors each cast a vote. Whichever class wins the majority becomes the prediction for the new point.
k Is the Key Choice
The letter k is how many neighbors you consult. It is the one knob that most shapes how kNN behaves.
Small k, Jumpy Borders
A tiny k, like 1, follows every wiggle in the data and reacts to noise, giving jagged, overfit boundaries.
Large k, Smoother Calls
A big k averages over many points for smoother decisions, but too large and it blurs the real differences between classes.
Scaling Is Not Optional
Distance is unfair if one feature spans thousands and another spans tenths. Always scale features so each counts equally.
Build the Classifier
Create it like any estimator and pick your n_neighbors right away. Here we consult the five closest points.
from sklearn.neighbors import KNeighborsClassifier
model = KNeighborsClassifier(n_neighbors=5)Fit, Then Predict
The familiar contract still applies: fit stores the data, predict finds neighbors and votes on the answer.
model.fit(X_train, y_train)
model.predict(X_test)Watch the Cost
kNN is simple but can be slow at prediction time, since every guess compares the new point to all stored examples.
Quick Check
Let's pin down the parameter that defines kNN.
Recap
kNN predicts by letting the closest k neighbors vote. Choose k with care and scale your features, and it works well. 🎯
Frequently asked questions
Is the “k-Nearest Neighbors” lesson free?
Yes — the full text of “k-Nearest Neighbors” is free to read here on the web, and the Data Science Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Data Science Academy course, upgrade to CoddyKit PRO.
What will I learn in “k-Nearest Neighbors”?
Classifying by closest examples. You practise Data Science Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Data Science Academy?
No prior experience is required. Data Science Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “k-Nearest Neighbors” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Data Science Academy lesson?
Yes. Every Data Science Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.