第十章想着一气看完把笔记发出来，结果！！看了好久都没看完没看懂，为了不打击我的积极性+ 赶进度，第十章后面的回头再看吧。。尴尬
正则表达式
library(tidyverse)
library(stringr)
基础
- 单引号/双引号来创建字符串
- 使用\对单引号或双引号进行”转义“
- 换行符 \n ，制表符\t
stringr函数
以str_开头，RStudio中处理字符串
字符串组合
合并两个字符串str_c("x", "y",sep = ",") [1] "x,y"
将字符向量合并为字符串 str_c(c("x","y","z"),collapse = ",") [1] "x,y,z"
字符串取子集
x <- c("apple","banana","pear")
str_sub(x,1,3)
[1] "app" "ban" "pea"
str_sub(x,-3,-1) # 负数表示从后往前数
[1] "ple" "ana" "ear"
- str_to_lower()文本转为小写
- str_to_upper()、str_to_title()文本转为大写
区域设置
查看维基百科中List of ISO 639-1 codes
-str_sort(x, locale = "en") #英语
p134练习题
- paste()和paste0() 的区别是前一个可以自定义分隔符
❌ || 答案: 前者中间默认有空格
paste("foo", "bar")
[1] "foo bar"
paste0("foo", "bar")
[1] "foobar"
str_c("foo", "bar")
[1] "foobar"
str_c与paste0的功能相似，但是str_c()中，NA具有传染性，paste和paste0两个函数将NA返回成字符
x <- "apple"
y <- "banana"
paste(x,y)
[1] "apple banana"
paste0(x,y)
[1] "applebanana"
z <- NA
paste0(x,z)
[1] "appleNA"
paste(x,z)
[1] "apple NA"
str_c(x,z)
[1] NA
- sep添加分隔符，collapse将字符向量合并成一个字符串
3.一开始 ceiling()函数的功能不了解
本来想先判断下是否是奇数个。。
x <- c("abc",'abcd')
n <- str_length(x)
m <- ceiling(n/2)
str_sub(x,m,m)
[1] "b" "b"
m <- floor(n/2)
str_sub(x,m,m)
[1] "a" "b"
- str_wrap()将字符串set到特定宽度，使得打印好看
str_wrap(string, width = 80, indent = 0, exdent = 0) - str_trim()修剪字符串中的空白
str_trim(" abc ")
#> [1] "abc"
str_trim(" abc ", side = "left")
#> [1] "abc "
str_trim(" abc ", side = "right")
#> [1] " abc"
与str_trim相反的是str_pad()
str_pad("abc", 5, side = "both")
#> [1] " abc "
str_pad("abc", 4, side = "right")
#> [1] "abc "
str_pad("abc", 4, side = "left")
#> [1] " abc"
模式匹配
str_view()和str_view_all()：接手一个字符向量和一个正则表达式，并显示如何匹配的。
x <- c("apple", "banana","pear")
str_view(x,"an")
x <- c("apple", "banana","pear")
str_view(x,".a.") # .匹配任意字符
匹配. 的正则表达式是.，字符串是\.。
p136 练习题
1."": This will escape the next character in the R string.
"\": This will resolve to \ in the regular expression, which will escape the next character in the regular expression.
"\": The first two backslashes will resolve to a literal backslash in the regular expression, the third will escape the next character. So in the regular expression, this will escape some escaped character.
- ""'\" ❌ 答案
str_view("\"'\\", "\"'\\\\")
✔️str_view("\"'\\\", "\"'\\\\\")也可以 - 点后面的任何字母都能匹配
？？？不是很理解
锚点
- ^ 从字符串开头进行匹配
- $从字符串末尾开始匹配
- \b匹配单词边界
p137练习题
- str_view("
", "\$\\$$")
str_view(stringr::words, "^y", match =TRUE)
str_view(stringr::words, "x$", match = TRUE)
str_view(stringr::words, "^...$", match = TRUE)
str_view(stringr::words, ".......", match = TRUE)
字符选项
- \d
- \s 匹配任意空白字符
- [abc] 匹配成a,b,c
- [^abc] 匹配成除a,b,c以外的任意字符
p138 练习题
1.
①
str_view(stringr::words, "^a|e|i|o|u", match =TRUE)
Error in loadNamespace(name) : there is no package called ‘htmlwidgets’
install.packages("htmlwidgets")
str_view(stringr::words, "^a|e|i|o|u", match =TRUE)
|| 答案：str_view(stringr::words, "^[aeiou]", match = TRUE)
②
str_view(stringr::words, "[^aeiou]", match =TRUE)
able
about
absolute
accept
account
achieve
across
...
|| 答案
str_view(stringr::words, "^[^aeiou]+$", match=TRUE)
符号+ 去掉之后，结果为空白，稍后章节会解释其含义
③
str_view(stringr::words, "ed$| [^eed$]", match=TRUE)
bed
feed
hundred
indeed
need
proceed
red
speed
...
×|| 答案：
str_view(stringr::words, "^ed$|[^e]ed$", match = TRUE)
④
str_view(stringr::words, "ing$|ize$", match = TRUE)
bring
during
evening
king
meaning
morning
organize
recognize
ring
thing
|| 答案：str_view(stringr::words, "i(ng|se)$", match = TRUE)
2
str_view(stringr::words, "(cei|[^c]ie)", match = TRUE)
找到a) c在前面，i在e后面 b)i在e前面，i前面是非c的单词
str_view(stringr::words, "(cie|[^c]ei)", match = TRUE)
sum(str_detect(stringr::words, "(cei|[^c]ie)"))
sum(str_detect(stringr::words, "(cie|[^c]ei)"))
3
str_view(stringr::words, "q[^u]", match = TRUE)
在stringr::words里是的
4
“ou” instead of “o”
use of “ae” and “oe” instead of “a” and “o”
ends in ise instead of ize
ends in yse
ou|ise$|ae|oe|yse$
黑人问号
5
答案中，美国
x <- c("123-456-7890", "1235-2351")
str_view(x, "\\d\\d\\d-\\d\\d\\d-\\d\\d\\d\\d")
str_view(x, "[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]")
str_view(x, "\\d{3}-\\d{3}-\\d{4}")
中国应该是 xxxx-xxxxxxxx
重复
控制一个模式匹配多次
- ?：0次或者多次‘
- +：1次或者多次
- *：0次或者多次
- {n};匹配n次
- {n,}: 匹配n次或者多次
- {,m}：最多匹配m次
- {n,m}:匹配n到m次
p139练习
1
?: {0,1}
+: {1,}
*:{0,}
2
① 匹配任意字符
② 匹配任意花括号里有至少一个字母的字符
③日期的表达，YYYY-MM-DD
④ \{4},会匹配4个反斜杠
3
a
str_view(stringr::words, "^[^aeiou]{3}", match=TRUE)
|| 答案: str_view(words, "^[^aeiou]{3}") 答案是不是错了。。。。
b
str_view(words, "[aeiou]{3,}")
???
c
str_view(words, "([aeiou][^aeiou]){2,}")
分组与回溯引用
()可定义“分组”
p140练习
不是很懂，用的时候再看吧。。。罪过
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