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Answers for “这段视频如何解释 PCA 选择保留哪些方向的方式?”

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Projecting onto the blue line loses less information because the spread along that direction is smaller. Clamping all points onto one line in that direction would not lose that much information.

Conditions: Demonstrated on a 2D scatter plot.; The explanation is geometric and intuitive rather than algebraic.

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The video states that dimensionality reduction is needed because data can have too many dimensions, which can often become a curse. Reducing the number of dimensions helps make the data more manageable and easier to process.

Conditions: Applies when data has many dimensions.; Presented as an introductory motivation, not as a formal theorem.