July 2018
Intermediate to advanced
596 pages
13h 35m
Japanese
Content preview from Pythonによるデータ分析入門 第2版 ―NumPy、pandasを使ったデータ処理
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11.6
再サンプリングと頻度変換
379
1961Q2 1.47
...
2007Q2 2.75
2007Q3 3.45
2007Q4 6.38
2008Q1 2.82
2008Q2 8.53
2008Q3 -3.16
2008Q4 -8.79
2009Q1 0.94
2009Q2 3.37
2009Q3 3.56
Freq: Q-DEC, Name: infl, Length: 203, dtype: float64
11.6
再サンプリングと頻度変換
再サンプリングとは、時系列をある頻度から別の頻度に変換することを言います。高い頻度のデー
タを集約して低い頻度のデータにすることをダウンサンプリングと言い、低い頻度から高い頻度の場
合は、アップサンプリングと言います。しかし、すべての再サンプリングがこれらの種類に当てはまる
わけではありません。例
えば、
W-WED
（毎週水曜日）から
W-FRI
（毎週金曜日）への変換は、アップサンプ
リングでもダウンサンプリングでもありません。
pandas
オブジェクトは
resample
メソッドを持っています。これは、すべての頻度の変換に役立つメ
ソッドです。
resample
は、
groupby
と似た
API
を持っています。
resample
を呼び出してグループ化した
後、集約のための関数を呼ぶこともできます。
In [208]: rng = pd.date_range('2000-01-01', periods=100, freq='D')
In [209]: ts = pd.Series(np.random.randn(len(rng)), ...
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