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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322
10
章 データの集約とグループ演算
このインデックス参照で戻されるオブジェクトは、リストや配列を与えたときにはグループ化された
データフレームになり、スカラーとして単独の列名を与えた場合には、グループ化されたシリーズにな
ります。
In [32]: s_grouped = df.groupby(['key1', 'key2'])['data2']
In [33]: s_grouped
Out[33]: <pandas.core.groupby.SeriesGroupBy object at 0x7faa30c78da0>
In [34]: s_grouped.mean()
Out[34]:
key1 key2
a one 1.319920
two 0.092908
b one 0.281746
two 0.769023
Name: data2, dtype: float64
10.1.3
ディクショナリやシリーズのグループ化
グループ化の情報は、配列以外の形式の場合もあります。先ほどとは別のデータフレームの例を見
てみましょう。
In [35]: people = pd.DataFrame(np.random.randn(5, 5),
....: columns=['a', 'b', 'c', 'd', 'e'],
....: index=['Joe', 'Steve', 'Wes', 'Jim', 'Travis'])
In [36]: people.iloc[2:3, [1, 2]] = np.nan ...
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