April 2020
Intermediate to advanced
816 pages
18h 32m
Chinese
Content preview from 精通機器學習
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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.
229
第九章
無監督學習技術
雖然目前被實際使用的機器學習大都採用監督學習
（
因此
，
它也吸引大多數的資金
），
但
絕大多數可用的資料都是不平衡的
：
雖然我們有輸入特徵
X，
卻沒有標籤
y。
計算機科學
家
Yann LeCun
有句名言
「
如果智慧是塊蛋糕
，
那麼無監督學習就是蛋糕
，
監督學習是蛋
糕的糖衣
，
強化學習是蛋糕上面的櫻桃
。」
換句話說
，
無監督學習還隱藏著巨大的潛力
，
我們只接觸了冰山的一角
。
假設你要製作一個系統
，
讓它幫生產線上的每個產品拍幾張照片
，
並檢查哪些產品有缺
陷
。
你很容易就可以做出自動拍照的系統
，
每天可以拍下上千張照片
，
接著你可以在幾
週之內做出一個龐大的資料組
…
等一下
，
但它沒有標籤
！
如果你想要訓練一般的二元分類
器
，
讓它預測產品有沒有缺陷
，
你就要將每一張照片標為
「
有缺陷
」
或
「
正常
」，
通常要
聘請人類專家坐下來親自查看每一張照片
。
這是一種漫長
、
昂貴且無聊的工作
，
所以通常
只能處理所有可用的照片中的一小部分
。
因此
，
有標籤的資料組將會非常小
，
且分類器的
效果將令人失望
。
而且
，
每當公司改變它的產品時
，
整個程序就必須重新做一遍
。
如果演
算法可以直接利用無標籤的資料
，
不需要由人類幫每張照片加上標籤
，
豈不美哉
？
我們來
看無監督學習
。
第
8
章曾經介紹最常見的無監督學習任務
：
降維
。
本章將介紹其他無監督學習任務和
演算法
：
分群法（clustering）
目的是將相似的實例聚成一組
。
分群法很適合用於資料分析
、
顧客細分
、
推薦系統
、
搜尋引擎
、
圖像分割
、
半監督學習
、
降維
，
及其他
。
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and much more.
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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.