August 2017
Intermediate to advanced
500 pages
12h 3m
Japanese
Content preview from PythonとJavaScriptではじめるデータビジュアライゼーション
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204
9 章 pandas によるデータのクリーニング
9.4.2
文字列の置換
空の文字列を
NaN
に置換し、カウントされないようにします
†
。それには
pandas
の
replace
メ
ソッドが最適です。
DataFrame
全体にも個々の
Series
にも適用できます。
import numpy as np
bi_col.replace('', np.nan, inplace=True)
bi_col
Out:
0 NaN #
❶
1 Bosnia and Herzegovina
2 Bosnia and Herzegovina
3 NaN
...
bi_col.count()
Out: 142 #
❷
❶ 空の
''
文字列が
NumPy
の
NaN
に置き換えられている。
❷ 空の文字列とは異なり、
NaN
フィールドはカウントされない。
空の文字列を
NaN
に置き換えると、
born_in
フィールドの正しい数
142
が得られます。
DataFrame
のすべての空の文字列をカウントされない
NaN
に置き換えましょう。
df.replace('', np.nan, inplace=True)
pandas
では列内の文字列（およびその他のオブジェクト）の高度な置換が可能です（例えば、
正規表現（
https://ja.wikipedia.org/wiki/
正規表現）を作成でき、
Series
（通常は
DataFrame
列）
全体に適用します）。ノーベル賞
DataFrame
のアスタリスクが付いた名前を使った例を調べてみま
しょう。
例
9-2
で一部のノーベル賞名にアスタリスクが付いていることがわかり、その受賞者は受賞時 ...
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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.
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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.