regex - 在 R 中使用正则表达式从电子邮件中提取名称

Question

我有一个字符串 - 这是电子邮件链，我需要提取发件人的姓名 (From :)。在下面找到电子邮件示例

str1 <- 'From : Wendy YEOW (SLA) To : xxxx@lt.org Subject : RE: OneService@S
From: SLA Enquiry (SLA) Sent: Friday, 5 June, 2015 5:26 PM To : xxxx@lt.org Subject : RE: OneService@S 
From: Siti Zaharah RAMAN (ARKS) Sent: Friday, 5 June, 2015 5:26 PM To : xxxx@lt.org Subject : RE: OneService@S 
From: SLA Enquiry (SLA) Sent: Friday, 5 June, 2015 5:26 PM To : xxxx@lt.org Subject : RE: OneService@S 
From: Chin Hwang LAU (TA) Sent: Friday, 5 June, 2015 5:26 PM To : xxxx@lt.org Subject : RE: OneService@S'

我有以下代码 - 提取名称

str_extract_all(string=str1,pattern="\\b(From\\s*[:]+\\s*(\\w*))\\b")[[1]]
[1] "From : Wendy" "From: SLA"    "From: Siti"   "From: SLA"    "From: Chin"

但我想要的输出是:

[1] "Wendy YEOW (SLA)"    "SLA Enquiry (SLA)"    "Siti Zaharah RAMAN (ARKS)"   "SLA Enquiry (SLA)"    "Chin Hwang LAU (TA)"

Answer 1

您可以使用strsplit。这里不需要 gsub。

strsplit(str1, "From ?: | (To|Sent) ?:.*?(\\nFrom ?: |$)")[[1]][-1]
# [1] "Wendy YEOW (SLA)"          "SLA Enquiry (SLA)"         "Siti Zaharah RAMAN (ARKS)"
# [4] "SLA Enquiry (SLA)"         "Chin Hwang LAU (TA)"  

正则表达式基本上由两部分组成:

1. "From ?: ":这是字符串的开头。拆分返回空字符串和原始字符串的其余部分。
2. "(To|Sent) ?:.*?(\\nFrom ?: |$)":此正则表达式表示名称后的文本。它包括以 "To" 或 "Sent" 开头并以换行符 ("\\n") 结尾的子字符串，后跟下一个 "From" 或字符串结尾 ("$").

最后，[-1] 是删除空字符串所必需的(在第一个 “From” 之前)。