Once data are available as matrices of numbers where no data are missing anymore, data transformations are commonly applied. Some common transformations are reported in the following table.

Name | Description |
---|---|

Center | To bring the expected mean values back to zero. |

Scale | To remove the effect of the scale. |

Recalibrate | To emphasize, e.g., small or large values. |

Normalize | To center and bring values onto comparable scales. |

Indicator | To extract a single level or value from a variable. |

Quantile | To disregard value differences but keep order. |

Tf-idf | Each wordโs contribution is weighted as a function of the term frequency (tf) and its inverse frequency in all text documents (idf) |

The transformed numbers compose the set of predictor (or independent) variables, which statistical methods rely upon to build statistical models.

## References

- By Inductiveload [Public domain]