Convert an n*2 array (CSV) to a JSON file.

csv2json.py

#!/usr/bin/env python3
import json
from io import StringIO
import pandas as pd


def csv_to_json(csv_in):
    """Convert an n*2 array (CSV) to a JSON file.
    """
    # Load CSV data
    df = pd.read_csv(csv_in, usecols=['category', 'subcategory']).dropna()

    cat_sub_dict = {}  # Initialize category-subcategory dictionary.
    cats_already_added = set()  # Initialize checklist (check-set)
    for rec in df.to_dict(orient='records'):
        cat = rec['category']
        sub = rec['subcategory']
        # Category(cat) appears for the first time
        if cat not in cats_already_added:
            cat_sub_dict[cat] = [sub]
        # If the key 'cat' is already defined in the dictionary.
        else:
            cat_sub_dict[cat].append(sub)

        cats_already_added.update(cat)  # Update the checklist.
    # https://qiita.com/Hyperion13fleet/items/7129623ab32bdcc6e203
    out_file = 'sample.json'
    with open(out_file, 'w') as f:
        json.dump(
            cat_sub_dict, f,
            ensure_ascii=False,
            indent=2,
            sort_keys=True
        )
    print(f'Saved: {out_file}')


if __name__ == '__main__':
    pseudo_csv = StringIO('category,subcategory\nA,p\nA,q\nA,r\nB,x\nB,y\nB,z')
    csv_to_json(csv_in=pseudo_csv)