Problem Statement

A template for data is an arbitrarily nested tree of integer indices. Data payloads are given as a separate mapping, array or other simpler, flat, association of indices to individual items of data, and are strings. The idea is to create a data structure with the templates' nesting, and the payload corresponding to each index appearing at the position of each index. Answers using simple string replacement or regexp are to be avoided. The idea is to use the native, or usual implementation of lists/tuples etc of the language and to hierarchically traverse the template to generate the output. Given the following input template t and list of payloads p: The correct output should have the following structure, (although spacing and linefeeds may differ, the nesting and order should follow):

1. Generate the output for the above template, t.
2. Show which payloads remain unused.
3. Give some indication/handling of indices without a payload. Show output on this page.

Let's start with the solution:

fill_template <- function(x, template, prefix = "Payload#") {
  for (i in seq_along(template)) {
    temp_slice <- template[[i]]
    if (is.list(temp_slice)) {
      template[[i]] <- fill_template(x, temp_slice, prefix)
    } else {
      temp_slice <- paste0(prefix, temp_slice)
      template[[i]] <- x[match(temp_slice, x)]
    }
  }
  return(template)
}

library("jsonlite") # for printing the template and result
template <- list(list(c(1, 2), c(3, 4), 5))
payload  <- paste0("Payload#", 0:6)
result   <- fill_template(payload, template)

cat(sprintf(
  "Template\t%s\nPayload\t%s\nResult\t%s", 
  toJSON(template, auto_unbox = TRUE),
  toJSON(payload, auto_unbox = TRUE),
  toJSON(result, auto_unbox = TRUE)
))