Question

PHP中的str_replace（和preg_replace）函数用替换字符串替换所有出现的搜索字符串。我最感兴趣的是，如果search和replace args是数组（在R中我们称之为向量），那么str_replace从每个数组（向量）获取一个值并使用他们在主题上搜索和替换。

换句话说，R（或某些R包）是否具有执行以下功能的功能：

string <- "The quick brown fox jumped over the lazy dog."
patterns     <- c("quick", "brown", "fox")
replacements <- c("slow",  "black", "bear")
xxx_replace_xxx(string, patterns, replacements)          ## ???
## [1] "The slow black bear jumped over the lazy dog."

所以我正在寻找像chartr这样的东西，但是对于搜索模式和任意数量字符的替换字符串。这不能通过对gsub()的一次调用来完成，因为replacement参数只能是一个字符串，请参阅?gsub。所以我目前的实现就像：

xxx_replace_xxx <- function(string, patterns, replacements) {
   for (i in seq_along(patterns))
      string <- gsub(patterns[i], replacements[i], string, fixed=TRUE)
   string
}

但是，如果length(patterns)很大，我正在寻找更快的东西 - 我需要处理大量数据，而且我对目前的结果不满意。

用于基准测试的示例性玩具数据：

string <- readLines("http://www.gutenberg.org/files/31536/31536-0.txt", encoding="UTF-8")
patterns <- c("jak", "to", "do", "z", "na", "i", "w", "za", "tu", "gdy",
   "po", "jest", "Tadeusz", "lub", "razem", "nas", "przy", "oczy", "czy",
   "sam", "u", "tylko", "bez", "ich", "Telimena", "Wojski", "jeszcze")
replacements <- paste0(patterns, rev(patterns))

Answer 1

使用PCRE代替固定匹配，我的机器上的时间约为1/3。

xxx_replace_xxx_pcre <- function(string, patterns, replacements) {
   for (i in seq_along(patterns))
      string <- gsub(patterns[i], replacements[i], string, perl=TRUE)
   string
}
system.time(x <- xxx_replace_xxx(string, patterns, replacements))
#    user  system elapsed 
#   0.491   0.000   0.491 
system.time(p <- xxx_replace_xxx_pcre(string, patterns, replacements))
#    user  system elapsed 
#   0.162   0.000   0.162 
identical(x,p)
# [1] TRUE

Answer 2

如果模式是由字符字符组成的固定字符串，如示例中所示，则此方法有效。 gsubfn与gsub类似，但replacment参数可以是字符串，列表，函数或proto对象。如果它是一个列表，就像这里一样，它将正则表达式的匹配与名称进行比较，对于找到的那些，它将用相应的值替换它们：

library(gsubfn)

gsubfn("\\b\\w+\\b", as.list(setNames(replacements, patterns)), string)
## [1] "The slow black bear jumped over the lazy dog."

Answer 3

使用stri_replace_*_all函数之一并将vectorize_all参数设置为FALSE，可以使用stringi＆gt; = 0.3-1来完成此操作：

library("stringi")
string <- "The quicker brown fox jumped over the lazy dog."
patterns     <- c("quick", "brown", "fox")
replacements <- c("slow",  "black", "bear")
stri_replace_all_fixed(string, patterns, replacements, vectorize_all=FALSE)
## [1] "The slower black bear jumped over the lazy dog."
stri_replace_all_regex(string, "\\b" %s+% patterns %s+% "\\b", replacements, vectorize_all=FALSE)
## [1] "The quicker black bear jumped over the lazy dog."

一些基准：

string <- readLines("http://www.gutenberg.org/files/31536/31536-0.txt", encoding="UTF-8")
patterns <- c("jak", "to", "do", "z", "na", "i", "w", "za", "tu", "gdy",
   "po", "jest", "Tadeusz", "lub", "razem", "nas", "przy", "oczy", "czy",
   "sam", "u", "tylko", "bez", "ich", "Telimena", "Wojski", "jeszcze")
replacements <- paste0(patterns, rev(patterns))
microbenchmark::microbenchmark(
   stri_replace_all_fixed(string, patterns, replacements, vectorize_all=FALSE),
   stri_replace_all_regex(string, "\\b" %s+% patterns %s+% "\\b", replacements, vectorize_all=FALSE),
   xxx_replace_xxx_pcre(string, "\\b" %s+% patterns %s+% "\\b", replacements),
   gsubfn("\\b\\w+\\b", as.list(setNames(replacements, patterns)), string),
   unit="relative",
   times=25
)
## Unit: relative
##                   expr       min        lq      mean    median        uq       max neval
## stri_replace_all_fixed  1.000000  1.000000  1.000000  1.000000  1.000000  1.000000    25 
## stri_replace_all_regex  2.169701  2.248115  2.198638  2.267935  2.267635  1.753289    25  
## xxx_replace_xxx_pcre    1.983135  1.967303  1.937021  1.961449  1.974422  1.469894    25  
## gsubfn                 63.067835 69.870657 69.815031 71.178841 72.503020 57.019072    25

因此，就字边界匹配而言，基于PCRE的版本是最快的。

将一组模式匹配替换为R中的相应替换字符串

3 个答案: