version_diff.R

version_diff <- function(old, new) {
  stopifnot(length(old) == length(new))
  
  if (length(old) > 1) {
    has_names <- !is.null(names(old))
    return(
      mapply(version_diff, old, new, SIMPLIFY = FALSE, USE.NAMES = has_names)
    )
  }
  
  as_pkg_version <- function(x) {
    if (inherits(x, "package_version")) return(x)
    package_version(x)
  }
  
  old <- as_pkg_version(old)
  new <- as_pkg_version(new)
  
  pad <- function(x, len) {
    if (length(x) >= len) return(x)
    c(x, rep(0, len - length(x)))
  }
  
  new <- unclass(new)[[1]]
  old <- unclass(old)[[1]]
  max_len <- max(length(new), length(old))
  
  diff <- pad(new, max_len) - pad(old, max_len)
  idx_first <- which(diff > 0)[[1]]
  diff <- pad(diff[1:idx_first], 3)
  
  package_version(paste(diff, collapse = "."))
}

version_diff(
  old = c(DT = "0.17", Rcpp = "1.0.7",   MASS = "7.3-51"),
  new = c(     "0.22",        "1.0.8.3",        "7.3-56")
)
#> $DT
#> [1] '0.5.0'
#> 
#> $Rcpp
#> [1] '0.0.1'
#> 
#> $MASS
#> [1] '0.0.5'

# https://gist.github.com/7d21aab922aec5d2b95675b7f611a256