A statistical method that extracts the main repeating patterns from data by reducing its dimensionality.Principal component analysis (PCA) is a statistical technique that reduces the dimensionality of a dataset while preserving as much of its variability as possible. It identifies the directions, called principal components, along which the data varies the most. The first principal component captures the largest variance, the second captures the next largest, and so on, with each component orthogonal to the previous ones. This transformation allows complex, high-dimensional data to be visualized and analyzed in a lower-dimensional space, often revealing hidden structure.
PCA was introduced by Karl Pearson in 1901 as a method for finding lines and planes that best fit a set of points. It was later formalized and popularized by Harold Hotelling in the 1930s, who applied it to psychometrics and economics.
PCA works by computing the covariance matrix of the data and then finding its eigenvectors and eigenvalues. The eigenvectors define the directions of maximum variance, and the eigenvalues give the amount of variance along each direction. By projecting the original data onto the top few eigenvectors, you obtain a compressed representation that retains most of the information. The process is equivalent to performing singular value decomposition on the data matrix.
PCA is widely used in image compression, facial recognition, genomics for analyzing gene expression data, and finance for risk management and portfolio optimization.
PCA is the mathematical foundation behind the 'eigenfaces' technique in facial recognition, where a face is represented as a combination of a few principal component images.







