In-place string substitution in R. Example: s("my name is $x and time is $y")

in_place_sub.R

s <- function(str) {
  
  require(stringr)
  require(magrittr)
  
  # helper functions
  get_vars  <- function(str) str %>% str_extract_all("\\$[a-zA-Z0-9_\\.]+") %>% unlist %>% str_replace_all("\\$","")
  eval_var  <- function(var) eval(parse(text = var)))
  add_token <- function(var) paste0("\\$", var)
  
  # replace a given var with its value in a string
  replace_var <- function(str,var) str %>% str_replace_all(add_token(var), eval_var(var))
  
  vars <- get_vars(str)
  
  # replace each variable with its value
  for(i in seq_along(vars))
    str <- replace_var(str, vars[i])
  
  str # return updated string
}

rows <- 22
duration.secs <- 60

s("($rows rows, $duration.secs s)")
# [1] "(22 rows, 60 s)"