AttributeError when using ColumnTransformer into a pipeline
This is my first machine learning project and the first time that I use ColumnTransformer. My aim is to perform two steps of data preprocessing, and use ColumnTransformer for each of them. In the first step, I want to replace the missing values in my dataframe with the string 'missing_value' for some features, and the most frequent value for the remaining features. Therefore, I combine these two operations using ColumnTransformer and passing to it the corresponding columns of my dataframe. In the second step, I want to use the just preprocessed data and apply OrdinalEncoder or OneHotEncoder