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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10.1
GroupBy
の仕組み
323
In [39]: by_column = people.groupby(mapping, axis=1)
In [40]: by_column.sum()
Out[40]:
blue red
Joe 0.503905 1.063885
Steve 1.297183 -1.553778
Wes -1.021228 -1.116829
Jim 0.524712 1.770545
Travis -4.230992 -2.405455
シリーズも固定サイズのマッピングとみなせるため、
groupby
に渡して使うことができます。
In [41]: map_series = pd.Series(mapping)
In [42]: map_series
Out[42]:
a red
b red
c bl
ue
d blue
e red
f orange
dtype: object
In [43]: people.groupby(map_series, axis=1).count()
Out[43]:
blue red
Joe 2 3
Steve 2 3
Wes 1 2
Jim 2 3
Travis 2 3
10.1.4
関数を使ったグループ化
ディクショナリやシリーズを使ったグループ化方式と比べて、
Python
の関数を使う方法は、より汎
用的です。グループキーとして渡される関数は、インデックスの値ごとに呼び出され、戻り値がグルー
プ名として用いられます。より具体的に説明するために、先ほど例として使ったデータフレ
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