fit_transform_on_test.md

Effect

Overesteemed results.

Rules to avoid leakage

1. Clearly separate train and test dataset
2. Use pipelines for fit_transform and transform

Quick fix example

X_train_transformed = pipeline.fit_transform(X_train)
X_test_transformed = pipeline.transform(X_test)

Incorporation stage

Modeling.

Locate in code

Change of test data prior training