regex - R 正则表达式 - 替换第 n 个匹配项

Question

假设你想用向量替换中的第二个元素替换第二个字符串匹配。例如:

x <- "CBCADEFGHI"
pattern <- "(A|D|C)"
replacement <- c("X","Y","Z")

您将如何仅用相应的替换向量元素“Z”替换第二个模式匹配，即“C”，因为它是发现的第二个模式？

期望的输出:

"CBZADEFGHI"

Answer 1

希望我理解正确。这是我的想法。

## find the position of the second match
g <- gregexpr(pattern, x)[[1]][2]
## get the individual letter elements out of 'pattern'
s <- scan(text = gsub("[()]", "", pattern), sep = "|", what = "")
## replace the position 'g' in 'x' with the matched element in 'replacement'
substr(x, g, g) <- replacement[match(substr(x, g, g), s)]
## resulting in
x
# [1] "CBZADEFGHI"