Python | 標準ライブラリ（csv + pathlib + collections + datetime）だけ を使って、CSVを「商品ごと × 日付ごと」にクロス集計する実践例

import csv
from pathlib import Path
from collections import defaultdict
from datetime import datetime

csv_path = Path.home() / "Documents" / "sales.csv"

# 集計用: {商品: {日付: {"数量":合計, "金額":合計}}}
summary = defaultdict(lambda: defaultdict(lambda: {"数量": 0, "金額": 0}))

with csv_path.open("r", encoding="utf-8") as f:
    reader = csv.DictReader(f)
    for row in reader:
        date = datetime.strptime(row["日付"], "%Y-%m-%d").date()
        product = row["商品"]
        qty = int(row["数量"])
        price = int(row["金額"])
        summary[product][date]["数量"] += qty
        summary[product][date]["金額"] += price

# 表示（商品ごとに日付順で出力）
for product, dates in summary.items():
    print(f"=== {product} ===")
    for date, data in sorted(dates.items()):
        print(f"{date}: 数量={data['数量']}, 金額={data['金額']}")

import csv
from pathlib import Path
from collections import defaultdict
from datetime import datetime

csv_path = Path.home() / "Documents" / "sales.csv"

# 集計用: {商品: {日付: {"数量":合計, "金額":合計}}}
summary = defaultdict(lambda: defaultdict(lambda: {"数量": 0, "金額": 0}))

with csv_path.open("r", encoding="utf-8") as f:
    reader = csv.DictReader(f)
    for row in reader:
        date = datetime.strptime(row["日付"], "%Y-%m-%d").date()
        product = row["商品"]
        qty = int(row["数量"])
        price = int(row["金額"])
        summary[product][date]["数量"] += qty
        summary[product][date]["金額"] += price

# 表示（商品ごとに日付順で出力）
for product, dates in summary.items():
    print(f"=== {product} ===")
    for date, data in sorted(dates.items()):
        print(f"{date}: 数量={data['数量']}, 金額={data['金額']}")

output_path = csv_path.parent / "cross_summary.csv"

# 全日付を抽出してソート
all_dates = sorted({date for dates in summary.values() for date in dates})

with output_path.open("w", newline="", encoding="utf-8") as f:
    writer = csv.writer(f)
    # ヘッダー行: 商品, 各日付
    writer.writerow(["商品"] + [d.isoformat() for d in all_dates])
    for product, dates in summary.items():
        row = [product]
        for d in all_dates:
            row.append(dates[d]["数量"] if d in dates else 0)
        writer.writerow(row)

print("クロス集計を保存しました:", output_path)

output_path = csv_path.parent / "cross_summary.csv"

# 全日付を抽出してソート
all_dates = sorted({date for dates in summary.values() for date in dates})

with output_path.open("w", newline="", encoding="utf-8") as f:
    writer = csv.writer(f)
    # ヘッダー行: 商品, 各日付
    writer.writerow(["商品"] + [d.isoformat() for d in all_dates])
    for product, dates in summary.items():
        row = [product]
        for d in all_dates:
            row.append(dates[d]["数量"] if d in dates else 0)
        writer.writerow(row)

print("クロス集計を保存しました:", output_path)