使用R中的gsub在子字符串周围插入点

Question

我想在R中有一个函数,如果它们尚不存在,则在给定的子字符串(例如"alpha")周围插入点(".").例如 string="10-alpha-epoxy-Amorph-4-ene"应该返回

"10-.alpha.-epoxy-Amorph-4-ene"

string="alpha-cadolene" 应该回来

".alpha.-cadolene"

但 string=".alpha.-cadolene"应该回来

".alpha.-cadolene"

(子串可能会多次出现)

在R中使用gsub实现这一目标的最简单方法是什么？

汤姆,欢呼声

Answer 1

我会做这样的事情:

gsub("[.]?(alpha)[.]?", ".\\1.", c("10-alpha-epoxy-Amorph-4-ene",
                               ".alpha.-cadolene", "alpha.-cadolene",
                                ".alpha-cadolene"                              
                                 ))
[1] "10-.alpha.-epoxy-Amorph-4-ene" ".alpha.-cadolene"             
    ".alpha.-cadolene"              ".alpha.-cadolene"  

编辑泛化到许多术语:

如果您有术语列表,可以使用create tour正则表达式paste:

terms <- c('alpha','gamma','beta','delta')

gsub(paste0("[.]?(",paste0(terms,collapse='|'),")[.]?"), ".\\1.", 
                c("10-alpha-epoxy-Amorph-4-ene",
                 ".gamma.-cadolene", "beta.-cadolene",
                 ".delta-cadolene")) 

[1] "10-.alpha.-epoxy-Amorph-4-ene" ".gamma.-cadolene"             
    ".beta.-cadolene"              
[4] ".delta.-cadolene"  

编辑以完整的字母获取greels列表:

library(XML)
dat <- readHTMLTable("http://en.wikipedia.org/wiki/Greek_alphabet",
                     strinsAsFactors=FALSE)[[2]]

terms <- as.character(dat$V2[-c(1,2)])
 [1] "alpha"   "beta"    "gamma"   "delta"   "epsilon" "zeta"    "eta"     "theta"   "iota"    "kappa"   "lambda" 
[12] "mu"      "Name"    "Modern"  "nu"      "xi"      "omicron" "pi"      "rho"     "sigma"   "tau"     "upsilon"
[23] "phi"     "chi"     "psi"     "omega"