January 2020
Beginner to intermediate
728 pages
10h 26m
Japanese
Content preview from データサイエンス設計マニュアル
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10.2 最近傍分類 289
図 10 -4 k 近
傍法を使った性別の決定境界に k が与える影響。k = 3（左）、k = 10（右）、k = 1（図 10 -3）
を比較してみよう
図 10 -5 最近傍探索のためのデータ構造としてはボロノイ図（左）
、kd 木（右）などがある
10.2.3 最近傍点の探索
最近傍分類の最大の問題は、おそらく実行時にコストがかかる。
d
次元空間で与えられた点
q
と
n
個の同
様の訓練点の比較を最も自明な方法で行えば、n 回の明示的な距離計算を実行することになるので、O(nd)
のコストがかかる。どんな分類システムでも、数千、いや数百万の訓練点を対象としてこのような探索を行
えば、はっきりと認識されるタイムラグが生まれる。
この探索を高速化するためのアプローチとしては、幾何学的なデータ構造を使うものがある。よく使われ
ているのは次のようなものである。
• ボロノイ図：一連のターゲット点を囲むように空間を分割し、個々のセルにターゲット点が 1 つず
290 10 章 ネットワーク分析と距離
図 10 -6 グ
リッドインデックスデータ構造は、点が一様に分布していれば、最近傍点へ高速にアクセスで
きるが、一部の領域の点が密なクラスタを形成しているときには、非効率になる恐れがある
つ含まれるようにする。さらに、セル内のどの位置にいても、最近傍のターゲット点が自分のセルの ...
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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.
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.