从R中的字符串中提取模式，而无需区分大小写字母 [英] Extract pattern from string in R without distinguishing between upper and lower case letters

问题描述

这是一个玩具示例.我想在 a 中搜索并提取在 b 中列出的那些颜色.即使颜色不是以大写字母开头，我也要提取它.但是，输出应该告诉我 a 中颜色的使用方式.

This is a toy example. I want to search within a and extract those colors that are listed in b. Even if the color does not start with an upper case letter, I want to extract it. However, the output should tell me how the color was used in a.

所以我想得到的答案是#"Red" NA"blue .

So the answer I would like to get is #"Red" NA "blue.

a <- "She has Red hair and blue eyes"
b <- c("Red", "Yellow", "Blue")
str_extract(a, b)#"Red" NA    NA

我使用了'stringr'中的 str_extract ，但很乐意使用其他函数/包(例如 grep ).

I used str_extract from 'stringr', but would be happy to use another function/package (e.g., grep).

推荐答案

我们可以在 base R

unlist(sapply(tolower(b), function(x) {
        x1 <- regmatches(a, gregexpr(x, tolower(a)))
      replace(x1, x1 == "character(0)", NA)}), use.names=FALSE)
# "Red"     NA "blue" 

或者从@leerssej的答案中得到启发

Or as inspired from @leerssej's answer

library(stringr)
str_extract(a, fixed(b, ignore_case=TRUE))
#[1] "Red"  NA     "blue"

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