Unsupervised dimensionality reduction via principal component analysis 128 Total and explained variance Feature transformation Principal component analysis in scikit-learn Supervised data compression via linear discriminant analysis Computing the scatter matrices Selecting linear discriminants for the new feature subspace Projecting samples onto the new feature space LDA via scikit-learn Using kernel principal component analysis for nonlinear mappings Kernel functions and the kernel trick Implementing a kernel principal component analysis in Python Example 1 – separating half-moon shapes Example 2 – separating concentric circles Projecting new data points Kernel principal component analysis in scikit-learn Summary