sklearn Pipeline: argument of type 'ColumnTransformer' is not iterable
问题 I am attempting to use a pipeline to feed an ensemble voting classifier as I want the ensemble learner to use models that train on different feature sets. For this purpose, I followed the tutorial available at [1]. Following is the code that I could develop so far. y = df1.index x = preprocessing.scale(df1) phy_features = ['A', 'B', 'C'] phy_transformer = Pipeline(steps=[('imputer', SimpleImputer(strategy='median')), ('scaler', StandardScaler())]) phy_processer = ColumnTransformer