学ぶ Efficient Data Preprocessing with Pipelines

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With the ability to transform columns separately using the make_column_transformer function, the next step is to build pipelines. A pipeline is a container that organizes preprocessing steps and applies them sequentially.

A pipeline in Scikit-learn can be created using either the Pipeline class constructor or the make_pipeline function from the sklearn.pipeline module. This course will focus on make_pipeline, as it is simpler to apply.

You just need to pass all the transformers as arguments to a function. Creating pipelines is that simple.

However, when you call the .fit_transform(X) method on the Pipeline object, it applies .fit_transform(X) to every transformer inside the pipeline, so if you want to treat some columns differently, then you should use a ColumnTransformer and pass it to make_pipeline().

Build a pipeline using the same file as in the previous chapter. The pipeline should include encoders for categorical features along with SimpleImputer. Since the dataset contains both nominal and ordinal features, use a ColumnTransformer to process them separately.


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import pandas as pd
from sklearn.compose import make_column_transformer
from sklearn.preprocessing import OneHotEncoder, OrdinalEncoder
from sklearn.impute import SimpleImputer
from sklearn.pipeline import make_pipeline

df = pd.read_csv('https://codefinity-content-media.s3.eu-west-1.amazonaws.com/a65bbc96-309e-4df9-a790-a1eb8c815a1c/exams.csv')
# Making a column transformer
edu_categories = ['high school', 'some high school', 'some college', "associate's degree", "bachelor's degree", "master's degree"]
ct = make_column_transformer(
  (OrdinalEncoder(categories=[edu_categories]), ['parental level of education']),
  (OneHotEncoder(), ['gender', 'race/ethnicity', 'lunch', 'test preparation course']), 
  remainder='passthrough'
)
# Making a Pipeline
pipe = make_pipeline(ct, SimpleImputer(strategy='most_frequent'))
print(pipe.fit_transform(df))

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セクション 1. 章 19

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