What is the difference between feature selection and dimensionality reduction?

I know that both feature selection and dimensionality reduction aim towards reducing the number of features in the original set of features. What is the exact difference between the two if we are doing the same thing in both of them?

Answer

The difference is that the set of features made by feature selection must be a subset of the original set of features, and the set made by dimensionality reduction doesn’t have to (for instance PCA reduces dimensionality by making new synthetic features from linear combination of the original ones, and then discarding the less important ones).

This way feature selection is a special case of dimensionality reduction.

Attribution
Source : Link , Question Author : London guy , Answer Author : FairMiles

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