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
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
5.2
pandas
の重要な機能
171
5.2.8
重複したラベルを持つ軸のインデックス
ここまで見てきた例では、すべてのインデックスは一意なラベル（インデックス値）を持っていました。
reindex
のように、
pandas
の多くの関数ではインデックスのラベルが一意であることを要求しますが、
インデックスのラベル自体は一意である必要はありません。重複したインデックスを持つ小さなシリー
ズを考えてみましょう。
In [222]: obj = pd.Series(range(5), index=['a', 'a', 'b', 'b', 'c'])
In [223]: obj
Out[223]:
a 0
a 1
b 2
b 3
c 4
dtype: int64
インデックスの
is_unique
属性で、インデックスのラベルが一意かどうかを確認することができます。
In [224]: obj.index.is_unique
Out[224]: False
データの選択結果は、インデックスに重複があるときに振る舞いが変わる主な点です。重複したイ
ンデックスがある場合にはシリーズが戻されますが、重複がない場合にはスカラー値が戻されます。
In [225]: obj['a']
Out[225]:
a 0
a 1
dtype: int64
In [226]: obj['c']
Out[226]: 4
これによって、あなたのコードは複雑になるかもしれません。なぜなら、インデックス参照の結果で
得られるデータの型が、ラベルの重複の有無によって変わるから
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.