删除子文本数组之前的文本

Question

我有一组字符串需要操作。在每一个中，如果它们包含一组子字符串，我想保留子字符串，否则保持不变。

下面是一个例子：

keep <- c("USA","UNITED STATES")
keep <- paste0(paste0(" ",keep,"$"),collapse="|")

data <- c("DETROIT","DETROIT USA","DETROIT UNITED STATES")
expected_result <- c("DETROIT","USA","UNITED STATES")

Answer 1

您可以使用 str_extract 提取模式（如果存在）。这个 returns NA 以防模式丢失，你可以用原来的 data.

替换

keep <- c("USA","UNITED STATES")
keep <- paste0(paste0(" ",keep,"$"),collapse="|")

result <- stringr::str_extract(data, keep)
result[is.na(result)] <- data[is.na(result)]
trimws(result)
#[1] "DETROIT"       "USA"           "UNITED STATES"

Answer 2

您可以使用

data <- c("DETROIT","DETROIT USA","DETROIT UNITED STATES")
keep <- c("USA","UNITED STATES")

regex <- paste0(".*\s*\b(",paste0(keep,collapse="|"), ")\b")
sub(regex, "\1", data)
## => [1] "DETROIT"       "USA"           "UNITED STATES"

参见R demo online。

正则表达式为 .*\s*\b(USA|UNITED STATES)\b，参见 its online demo。

详情:

.* - 尽可能多的任意零个或多个字符
\s* - 零个或多个空格
\b(USA|UNITED STATES)\b - 整个单词 USA 或 UNITED STATES，捕获到第 1 组（替换模式中的）。

删除子文本数组之前的文本

Remove text before an array of subtexts

regex

substring

r

gsub

str-replace