August 2015
Intermediate to advanced
272 pages
5h 46m
Japanese
Content preview from Think Stats 第2版 ―プログラマのための統計入門
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17
2
章
分布
2.1
ヒストグラム
変数について記述する最良の方法は、データセットに出現する値と、その値の出現
回数を報告することです。この記述は、分布（
distribution
）と呼ばれます。
最も一般的な分布の表現はヒストグラム（
histogram
）です。ヒストグラムはそれ
ぞれの値の度数（
frequency
）を示すグラフです。この文脈での「度数」は、値が出
現する回数です。
Python
では、辞書（ディクショナリ）を使うと効率良く度数が求められます。例
えば
t
というシーケンスが与えられた場合、次のように記述します。
hist = {}
for x in t:
hist[x] = hist.get(x, 0) + 1
結果は値を度数にマップするディクショナリです。
collections
モジュールで定義
されている
Counter
クラスを代わりに使うこともできます。
from collections import Counter
counter = Counter(t)
結果は
Counter
オブジェクトで、ディクショナリの部分クラスです。
別の方法として、前章で出てきた、
pandas
のメソッド
value_counts
を使うことも
できます。本書では、クラス
Hist
を作りました。これは、ヒストグラムを表現し、
その上での操作のメソッドを提供します。
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