Data Standardization vs Normalization vs Robust Scaler
Am I right to say that also Standardization gets affected negatively by the extreme values as well?
Indeed you are; the scikit-learn docs themselves clearly warn for such a case:
However, when data contains outliers,
StandardScaler
can often be mislead. In such cases, it is better to use a scaler that is robust against outliers.
More or less, the same holds true for the MinMaxScaler
as well.
I really can't see how the Robust Scaler improved the data because I still have extreme values in the resulted data set? Any simple -complete interpretation?
Robust does not mean immune, or invulnerable, and the purpose of scaling is not to "remove" outliers and extreme values - this is a separate task with its own methodologies; this is again clearly mentioned in the relevant scikit-learn docs:
RobustScaler
[...] Note that the outliers themselves are still present in the transformed data. If a separate outlier clipping is desirable, a non-linear transformation is required (see below).
where the "see below" refers to the QuantileTransformer
and quantile_transform
.
None of them are robust in the sense that the scaling will take care of outliers and put them on a confined scale, that is no extreme values will appear.
You can consider options like:
- Clipping(say, between 5 percentile and 95 percentile) the series/array before scaling
- Taking transformations like square-root or logarithms, if clipping is not ideal
- Obviously, adding another column 'is clipped'/'logarithmic clipped amount' will reduce information loss.