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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188
6
章 データの読み込み、書き出しとファイル形式
6.1.1
テキストファイルを少しずつ読み込む
非常に巨大なファイルを処理する場合や、巨大ファイルを正しく処理するのにどのような引数を与え
る必要があるか調べる場合には、まずは
1
つのファイルのごく一部だけを読み込んだり、ファイル内の
小さなブロックごとに処理を繰り返したりしたいでしょう。
巨大なファイルを表示させる前に、
pandas
の表示の設定をもう少しコンパクトにしましょう。
In [33]: pd.options.display.max_rows = 10
次のような
10,000
行のデータがある
CSV
ファイルを例にします。
In [34]: result = pd.read_csv('examples/ex6.csv')
In [35]: result
Out[35]:
one two three four key
0 0.467976 -0.03
8649 -0.295344 -1.824726 L
1 -0.358893 1.404453 0.704965 -0.200638 B
2 -0.501840 0.659254 -0.421691 -0.057688 G
3 0.204886 1.074134 1.388361 -0.982404 R
4 0.354628 -0.133116 0.283763 -0.837063 Q
... ... ... ... ... ..
9995 2.311896 -0.417070 -1.409599 -0.515821 ...
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