正则表达式有条件地查找和替换

Question

我需要用字符串B替换字符串A,只有当字符串A是整个单词(例如"MECH")时,我不想在A是较长字符串的一部分时进行替换(例如"MECHANICAL") .到目前为止,我有一个grepl(),它检查字符串A是否是一个完整的字符串,但我无法弄清楚如何进行替换.我添加了一个ifelse(),当grep()返回TRUE时,想要更换gsub(),否则不要替换.有什么建议？请参阅下面的代码.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

from您可以将向量中的字符串括起来\\<并\\>仅匹配整个单词：

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"