问题描述
我正在尝试从我拥有的文档列表中提取名称。名称始终是最后一个第一个模式的第一个出现。
我正在使用stringr尝试以下正则表达式，但是它不起作用^ [A-Z] [a-z] +，\ s [A-Z] [a-z] + $ 我相信这是因为正则表达式之前的模式在整个文档中并不恒定。请参见下面的示例。
library(stringr)
m = c(" name: aaaaaa,bbbbbb age: 25","age 34 person: aaaa,bbbb"," location: A name
aaaa,bbbbbbb","aaaaa,bbbb")
str_extract(m,"^[A-Z][a-z]+,\\s[A-Z][a-z]+$")
# I tried to add a white space before and after the beginning of the pattern
# but still not working:
str_extract(m,"^\\s[A-Z][a-z]+,\\s[A-Z][a-z]+$\\s")
预期的输出是名称列表： aaaaaa，bbbbbb aaaa，bbbb aaaa，bbbbbbb aaaaa，bbbb
感谢您的建议。
解决方法
您的正则表达式似乎不太正确。尝试改用[A-Za-z]+,\s[A-Za-z]+，看看是否有区别。语句开头的“胡萝卜”字符仅与模式在行开头处开始的字符串匹配，而美元符号的末尾仅与在行末处结束的模式匹配。我还将A-Z和a-z组合并为一个，并删除了不必要的反斜杠。将来用RegExr之类的方法测试您的正则表达式可能会有所帮助，这样可以减轻重复运行程序的痛苦。
# Base example
m = c(" name: aaaaaa,bbbbbb age: 25","age 34 person: aaaa,bbbb"," location: A name aaaa,bbbbbbb")
# This function implement the solution
extract_lastfirst <- function(x) {
stopifnot(`"{stringr} is required"` = requireNamespace("stringr"))
stringr::str_extract(x,"\\w+,\\w+") # This line solve the problem
}
extract_lastfirst(m)
#> [1] "aaaaaa,bbbbbb" "aaaa,bbbb" "aaaa,bbbbbbb"
# In the text there is a mention to "the first occurrence of",so try
# the solution with an example the have a "second" occurrence.
n <- c("name: aa,bb wrong: cc,dd")
extract_lastfirst(n)
#> [1] "aa,bb"
# formal tests for the solution ---------------------------------------
# (no output means test passed)
library(testthat)
testthat::test_that("goal achieved",{
expected_out_m <- c("aaaaaa,bbbbbb","aaaa,bbbbbbb")
expect_equal(extract_lastfirst(m),expected_out_m)
})
testthat::test_that("multiple occurrences",{
expected_out_n <- c("aa,bb")
expect_equal(extract_lastfirst(n),expected_out_n)
})
由reprex package（v0.3.0）于2020-09-02创建
devtools::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#> setting value
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#> language (EN)
#> collate en_US.UTF-8
#> ctype en_US.UTF-8
#> tz Europe/Rome
#> date 2020-09-02
#>
#> ─ Packages ───────────────────────────────────────────────────────────────────
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#> stringi 1.4.6 2020-02-17 [1] CRAN (R 4.0.2)
#> stringr 1.4.0 2019-02-10 [1] CRAN (R 4.0.2)
#> testthat * 2.3.2 2020-03-02 [1] CRAN (R 4.0.2)
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#> withr 2.2.0 2020-04-20 [1] CRAN (R 4.0.2)
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#> yaml 2.2.1 2020-02-01 [1] CRAN (R 4.0.2)
#>
#> [1] /home/cl/R/x86_64-pc-linux-gnu-library/4.0
#> [2] /usr/local/lib/R/site-library
#> [3] /usr/lib/R/site-library
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