regex - 有条件地查找和替换的正则表达式

Question

我需要用字符串 B 替换字符串 A，仅当字符串 A 是一个完整的单词时(例如“MECH”)，并且当 A 是较长字符串的一部分(例如“MECHANICAL”)时，我不想进行替换.到目前为止，我有一个 grepl() 来检查字符串 A 是否是一个完整的字符串，但我不知道如何进行替换。我添加了一个 ifelse() 的想法是在 grep() 返回 TRUE 时替换 gsub()，否则不替换。有什么建议？请看下面的代码。谢谢。

aa <- data.frame(type = c("CONSTR", "MECH CONSTRUCTION", "MECHANICAL CONSTRUCTION MECH", "MECH CONSTR", "MECHCONSTRUCTION"))

from <- c("MECH", "MECHANICAL", "CONSTR",  "CONSTRUCTION")
to <- c("MECHANICAL", "MECHANICAL", "CONSTRUCTION", "CONSTRUCTION")

gsub2 <- function(pattern, replacement, x, ...) {
  for(i in 1:length(pattern)){
    reg <- paste0("(^", pattern[i], "$)|(^", pattern[i], " )|( ", pattern[i], "$)|( ", pattern[i], " )")
    ifelse(grepl(reg, aa$type),
           x <- gsub(pattern[i], replacement[i], x, ...),
           aa$type)
  }
  x
}

aa$title3 <- gsub2(from, to, aa$type)

Answer 1

您可以将字符串括在 from 中向量在 \\<和 \\>只匹配整个单词:

x <- c("CONSTR", "MECH CONSTRUCTION", "MECHANICAL CONSTRUCTION MECH", 
       "MECH CONSTR", "MECHCONSTRUCTION")

from <- c("\\<MECH\\>", "\\<CONSTR\\>")
to <- c("MECHANICAL", "CONSTRUCTION")

for(i in 1:length(from)){
  x <- gsub(from[i], to[i], x)
}

print(x)
# [1] "CONSTRUCTION"                       "MECHANICAL CONSTRUCTION"           
# [3] "MECHANICAL CONSTRUCTION MECHANICAL" "MECHANICAL CONSTRUCTION"           
# [5] "MECHCONSTRUCTION"