August 2022
Beginner to intermediate
436 pages
9h 43m
Korean
Content preview from SQL로 시작하는 데이터 분석
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345
6
장
이상 탐지
6.5.4
리스케일
이상값이 포함된 레코드를 필터링하거나 이상값을 다른 값으로 대체하는 방법 이외에, 필드를
리스케일하면 값이 모두 보존되고 분석도 더 쉬워집니다.
앞서
z
-점수 개념과 이를 활용한 아웃라이어 탐지를 살펴봤는데,
z
-점수는 양수와 음수를 모
두 다룰 수 있다는 장점을 활용해 값을 리스케일하는 데도 사용합니다.
z
-점수 대신 로그
log
스케일을 사용해 값을 변환하기도 합니다. 이때 모든 값의 상대적 크기가
그대로 보존된다는 장점이 있지만 작은 값들은 더 좁게 몰린다는 단점도 있습니다. 로그 변환
한 값은 필요시 원래 값으로 복구 가능합니다. 단점으로, 로그는 음수에는 사용할 수 없습니다.
earthquakes
데이터셋 저장된 지진 규모 값은 이미 로그 스케일이 적용된 값입니다. 동일본
대지진의 지진 규모는
9
.
1
로 매우 극단적인 값이지만, 로그 스케일을 적용하지 않았다면 훨씬
더 극단적으로 큰 아웃라이어 값이었을 것입니다.
depth
필드는 킬로미터 단위로 저장돼 있습니다. 다음 쿼리는 이 필드에
log
함수를 사용해
로그 스케일로 변환된 값을 나타냅니다. [그림
6
-
12
]와 [그림
6
-
13
]은 각각 로그 스케일을 적
용하기 전후의 지진 깊이 분포를 그래프로 보여줍니다.
log
함수에서 밑의 기본값은
10
입니
다. 그래프로 ...
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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.