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Principal component analysis (PCA) is a linear dimensionality reduction technique. It reduces a multivariate dataset to a smaller set of constructed variables preserving as much information (as much variance) as possible. These variables, called principal components, are linear combinations of the input variables.

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Making sense of principal component analysis, eigenvectors & eigenvalues

PCA is a technique to reduce dimension by: Taking linear combinations of the original variables. Each linear combination explains the most variance in the data it can. … I would never try to explain this to my grandmother, but if I had to talk generally about dimension reduction techniques, I'd point to this trivial projection example (not PCA). …
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