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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

Non-Mathy: The non-math explanation is that PCA helps for high dimensional data by letting you see in which directions your data has the most variance. These directions are the principal components. … Then in desperation you think to run PCA and discover the 90% of your variance comes from one direction, and that direction does not correspond to any of your axis. …
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