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.
|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 word’s 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.
- By Inductiveload [Public domain]