Insert a separator into a character vector containing two pieces of information where one piece has a constant width.

insert_sep.r

#==============================================================================#
# insert_sep.r Insert a separator into a character vector containing two pieces 
# of information where one piece has a constant width.
#
# Author: Zhian N. Kamvar
# License: GPLv3
# Year: 2014 
# Waranty: NONE
# 
# Arguments:
# string  = a character vector
# sep     = a character defining the separator.
# at      = the length of the fixed width information.
# forward = if TRUE, the fixed width information appears first. If FALSE, it
#           appears second.
#==============================================================================#
insert_sep <- function(string, sep = "_", at = 2, forward = TRUE){
  string_lengths <- nchar(string)
  if (!forward){
    at <- string_lengths - at
  }
  prefix <- substr(string, 1, at)
  suffix <- substr(string, at + 1, string_lengths)
  out_strings <- paste(prefix, suffix, sep = sep)
  return(out_strings)
}

# Generate data
forward <- vapply(1:length(letters), function(x) paste0(paste0(sample(LETTERS, 2), collapse = ""), sample(c("2000", "unknown"), 1, prob = c(0.9, 0.1))), character(1))
reverse <- vapply(1:length(letters), function(x) paste0(sample(c("2000", "unknown"), 1, prob = c(0.9, 0.1)), paste0(sample(LETTERS, 2), collapse = "")), character(1))

# Test
insert_sep(forward)
insert_sep(reverse, forward = FALSE)