从字符串最内层的嵌套括号中提取文本

Question

我试图从下面的文本字符串中提取特定的字符串子集。

string <- c("(Intercept)", "scale(AspectCos_30)", "scale(CanCov_500)", 
            "scale(DST50_30)", "scale(Ele_30)", "scale(NDVI_Tin_250)", "scale(Slope_500)", 
            "I(scale(Slope_500)^2)", "scale(SlopeVar_30)", "scale(CanCov_1000)", 
            "scale(NDVI_Tin_1000)", "scale(Slope_1000)", "I(scale(Slope_1000)^2)", 
            "scale(log(SlopeVar_30 + 0.001))", "scale(CanCov_30)", "scale(Slope_30)", 
            "I(scale(Slope_30)^2)")

一个好的结果是 return 中央文本没有任何特殊字符，如下所示。

Good <- c("Intercept", "AspectCos", "CanCov", "DST50", "Ele", "NDVI", "Slope", "Slope",
            "SlopeVar", "CanCov", "NDVI", "Slope", "Slope", "SlopeVar", "CanCov" "Slope", "Slope")

但是，生成的字符串最好分别说明与 'Slope' 和 'SlopeVar' 关联的 ^2 和 log。具体来说，所有包含 ^2 的字符串将被转换为 'SlopeSq'，所有包含 log 的字符串将被转换为 'SlopeVarPs'，如下所示。

Best <- c("Intercept", "AspectCos", "CanCov", "DST50", "Ele", "NDVI", "Slope", "SlopeSq",
          "SlopeVar", "CanCov", "NDVI", "Slope", "SlopeSq", "SlopeVarPs", "CanCov" "Slope", "SlopeSq")

我有一个冗长、丑陋且低效的代码序列，使我接近一半的好结果，我将不胜感激任何建议。

Answer 1

作为一个效率不高的编码员，我喜欢用多个正则表达式链来实现结果（每行正则表达式的作用在每一行中都有注释）：

library(stringr)
library(dplyr)
string %>% 
  str_replace_all(".*log\((.*?)(_.+?)?\).*", "\1Ps") %>% # deal with "log" entry
  str_replace_all(".*\((.*?\))", "\1") %>% # delete anything before the last "(" 
  str_replace_all("(_\d+)?\)\^2", "Sq") %>%  # take care of ^2
  str_replace_all("(_.+)?\)?", "") -> "outcome" # remove extra characters in the end (e.g. "_00" and ")")


Best <- c("Intercept", "AspectCos", "CanCov", "DST50", "Ele", "NDVI", "Slope", "SlopeSq",
          "SlopeVar", "CanCov", "NDVI", "Slope", "SlopeSq", "SlopeVarPs", "CanCov","Slope", "SlopeSq")
all(outcome == Best)
## TRUE

Answer 2

我认为这可以通过包 stringr 来实现。

首先，因为您想要最里面的括号内的 "central text"。因此，下面的正则表达式排除了括号内包含括号的任何文本。但是我保留了 "log/^2" 以备后用。

string_step <- str_extract(string,
                           "(log|)\([^()]+\)(\^2|)")

然后我注意到下划线之后的任何内容都被截断了，但只保留了字母（和数字）的短语。 Unlike \w (\w in R), which includes underscore, "[:alnum:]+" equals "[A-Za-z0-9]+"，因此被使用。

GoodMy <-
  str_extract(str_replace_all(string_step, "log|\(|\)|\^2", ""),
              "[:alnum:]+")

BestMy <-
  paste0(Good, as.character(sapply(string_step, function(x) {
    if (str_detect(x, "log")) {
      "Ps"
    } else if (str_detect(x, "\^2")) {
      "Sq"
    } else {
      ""
    }
  })))

all(Good == GoodMy, Best == BestMy) #yields True

从字符串最内层的嵌套括号中提取文本

Extract text from inner-most nested parentheses of string

regex

r

string-substitution