Machine Learning FAQ
What is Classification Report:

Precision
 What it means: Out of all the predictions your model made for a specific class (e.g., all the times it predicted “jazz”), precision tells you how many were actually correct.
 Example: If the model predicted “jazz” 10 times but only 6 of those were correct, precision would be
6 /10 = 0.6 (or 60%)
.

Recall
 What it means: Out of all the actual instances of a class in your dataset (e.g., how many times “jazz” really appears), recall tells you how many your model correctly identified.
 Example: If there are 8 “jazz” tracks, and your model correctly predicted 6 of them, recall would be
6 / 8 = 0.75 (or 75%)
.

F1Score
 What it means: The F1score is the harmonic mean of precision and recall. It’s a single metric that balances both. If you want to focus equally on precision and recall, F1score gives you a better picture.
 Example: If precision is 60% and recall is 75%, the F1score would be the combination of the two: F1 = 2 * ( (Precision * Recall) / (Precision + Recall) ) = ( 2 X (0.6 * 0.75) / (0.6 + 0.75) ) = 0.67

Support
 What it means: Support simply tells you how many actual instances of each class there are in the test data. It helps you see if your dataset is balanced or if some classes have more examples than others.
Example: Let’s look at a classification report snippet:
precision recall f1score support
blues 0.59 0.77 0.67 22
classical 0.90 0.93 0.91 28
country 0.59 0.59 0.59 22
 Blues Precision: Out of all the times the model predicted “blues,” 59% were correct.
 Blues Recall: Out of all the actual “blues” songs, the model correctly identified 77%.
 Blues F1Score: The F1score balances precision and recall, in this case, 67%.
 Support: There were 22 actual “blues” tracks in the validation set.
How It Helps:
 Precision is important when false positives (wrongly classifying something as a genre) are costly. For example, if you don’t want a “classical” song mistakenly predicted as “hiphop,” focus on precision.
 Recall is important when false negatives (missing instances of a genre) matter. For example, if it’s essential to catch all instances of “hiphop,” recall is critical.
The classification report helps you assess how well your model handles each class and where it struggles. You can also use it to compare models or finetune them.
Unsupervised Learning
In unsupervised learning, the machine is given a dataset that doesn’t have any labeled output. The goal is for the algorithm to find hidden patterns or relationships within the data on its own, without being told what the “right answer” is.
Example: Imagine you have a basket of mixed fruits, but you don’t know what types they are. An unsupervised learning algorithm would group similar fruits together based on features like size, color, and texture without knowing in advance which fruits are apples, oranges, etc.
Applications:
 Customer segmentation (grouping customers based on buying habits)
 Anomaly detection (finding unusual patterns)
 Data compression (dimensionality reduction)
KMeans Clustering
KMeans is a popular unsupervised learning algorithm used for clustering. Its purpose is to divide data points into K clusters, where each cluster contains similar data points.
How it Works:

Choosing K: You start by deciding how many clusters (K) you want to divide your data into.

Assigning Cluster Centers: The algorithm randomly selects K points in your dataset as initial cluster centers (centroids).

Assigning Points to Clusters: Each data point is assigned to the nearest centroid based on the distance (usually Euclidean distance). Points that are closer to a centroid are grouped into that cluster.

Recalculating Centroids: After all points are assigned, the algorithm recalculates the centroids of the clusters by finding the average of all points in each cluster.

Repeat: Steps 3 and 4 are repeated until the cluster assignments don’t change anymore (convergence).
Example: Let’s say you have a dataset of customers, and each customer has two features: total amount spent and frequency of visits. If you set K to 3, KMeans might group the customers into three clusters: high spenders who visit often, low spenders who visit rarely, and those in between.
Elbow Method
The Elbow Method helps determine the optimal number of clusters (K) in KMeans.
How it Works:

Run KMeans for different values of K (e.g., K=1, 2, 3, 4, etc.).

For each value of K, calculate the sum of squared distances (inertia) between data points and their assigned cluster centers. This tells you how tightly grouped your data points are within each cluster.

Plot the Inertia against the number of clusters (K). The graph will usually have a bend or elbow.

Optimal K: The point where the curve bends (the “elbow”) is considered the optimal K. Beyond this point, adding more clusters doesn’t improve the clustering significantly.
Example: Imagine you’re trying to segment customers into groups based on their purchasing patterns. By using the elbow method, you might find that the ideal number of clusters is 3, as the graph bends at K=3. Going beyond 3 clusters wouldn’t add much extra value.
ARIMA
ARIMA Model stands for AutoRegressive Integrated Moving Average. It is used to forecast future values in a time series, like predicting stock prices over time. Here’s a simplified version:
Key Concepts:

AutoRegressive (AR): This means that the model uses past values (previous stock prices) to predict future values. Think of it like this: if we know the stock price for the last few days, we might use those to predict what today’s price might be.
Example: If you knew that the stock price was $100 on Monday, $102 on Tuesday, and $104 on Wednesday, you might predict that it will increase similarly on Thursday.

Integrated (I): Sometimes, data might be moving up or down over time (like a trend). To make predictions easier, the ARIMA model removes that trend, making the data more “stationary” (flat). It does this by looking at the difference between one day’s price and the previous day’s price.
Example: If the stock price increases by $2 every day, the integrated part will take out that $2 jump so that it’s easier to see patterns in the changes.

Moving Average (MA): This part looks at the errors in past predictions. It tries to correct for those errors by considering the difference between predicted prices and actual prices in the past. So, if the model predicted wrong a few days ago, it adjusts itself for better predictions now.
Example: If you predicted that the stock would rise by $2 yesterday, but it only rose by $1, the model will use that mistake (error) to improve today’s prediction.
An Example:
Let’s say we want to predict the future price of a stock. Here’s how the ARIMA model would approach it:

AR (AutoRegressive): It looks at past prices like:
$100 on Monday $102 on Tuesday $104 on Wednesday It predicts that the price will be around $106 on Thursday, because it has been increasing by $2 each day.

I (Integrated): It looks at the changes in prices:
Monday to Tuesday: +$2 Tuesday to Wednesday: +$2 It calculates the differences and makes the data stationary (removing any trend).

MA (Moving Average): It checks how good its past predictions were and uses that info:
If it predicted $106 but the price was $105, it learns from the mistake and adjusts its future predictions.
Together, the ARIMA model combines these three steps to make a more accurate prediction for stock prices (or any timeseries data).