October 2017
Intermediate to advanced
480 pages
9h 49m
Japanese
Content preview from Rではじめるデータサイエンス
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11.3
正規表現でパターンマッチ
175
いか。エスケープして、正規表現
\\
を作るのです。この正規表現を作るには、文字列を使う必要が
あるので、そこでまたエスケープ
\
が必要となります。すなわち、
\
と文字通りマッチするには「
\\\\
」
とバックスラッシュを4 つ書きます。
x <- "a\\b"
writeLines(x)
#> a\b
str_view(x, "\\\\")
本書では正規表現を
\.
と書き、正規表現を表す文字列を
"\\."
または「
\\.
」と書きます。
1. なぜ
"\"
が、
"\"
,
"\\"
,
"\\\"
が
\
とマッチしないか説明しなさい。
2. 文字列
「
"'\
」
とはどうマッチするか。
3. 正規表現
\..\..\..
はどのようなパターンとマッチするか。文字列ではどう表すか。
11.3.2
アンカー
デフォルトでは、正規表現は文字列のどの部分ともマッチします。文字列の先頭または末尾に固
定（アンカーをつけた状態）してマッチするのが役立つこともあります。
●
^
は文字列の先頭とマッチする
●
$
は文字列の末尾とマッチする
x <- c("apple", "banana", "pear")
str_view(x, "^a")
str_view(x, "a$")
どちらがどちらか覚えるには、Evan Misshula（http://bit.ly/EvanMisshula）から学んだ次の句を
使ってみるとよいでしょう。「パワー（
^
）から始めれば、ダラー（
$
)で終わる。」
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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.