DOC Add detail about dataframe passthrough columns
@@ -83,9 +83,11 @@ class ColumnTransformer(TransformerMixin, _BaseComposition):
transformed and combined in the output, and the non-specified
columns are dropped. (default of ``'drop'``).
By specifying ``remainder='passthrough'``, all remaining columns that
- were not specified in `transformers` will be automatically passed
- through. This subset of columns is concatenated with the output of
- the transformers.
+ were not specified in `transformers`, but present in the data passed
+ to `fit` will be automatically passed through. This subset of columns
+ is concatenated with the output of the transformers. For dataframes,
+ extra columns not seen during `fit` will be excluded from the output
+ of `transform`.
By setting ``remainder`` to be an estimator, the remaining
non-specified columns will use the ``remainder`` estimator. The
estimator must support :term:`fit` and :term:`transform`.
