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Preprocess, Train and Evaluate a Model
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Preprocess, Train and Evaluate a Model

HardPython

Problem

Given a dataset, write the preprocessing and cleaning code, train a simple model in a framework of your choice, and report evaluation metrics (craft exercise)

Asked in the craft exercise stage. This is a multi-part, two-page prompt in CoderPad. Emphasise presentation of results and next steps.

Implement train_model(dataset, target_key). Each dataset row is a dictionary containing numeric feature values, with missing values represented by null, and a binary target. Remove exact duplicate rows, discard rows with a missing target, impute missing numeric features using training-set means, standardize features, and train a nearest-centroid classifier. Use a deterministic stratified holdout containing the last row from each class. Return accuracy, precision, recall, and F1, rounded to four decimal places.

Constraints

  • Each row is a dictionary with at least one numeric feature.
  • The target is 0 or 1 when present.
  • Each class has at least two valid rows after cleaning.
  • Missing feature values are represented by null.
  • Use only the Python standard library.

Function Signature

def train_model(dataset, target_key):
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