A python-style enumerate function for R.

enumerate.R

enumerate <- function(X, FUN, ...) {
  result <- vector("list", length(X))
  for (i in seq_along(result)) {
    tmp <- FUN(X[[i]], i, ...)
    if (is.null(tmp))
      result[i] <- list(NULL)
    else
      result[[i]] <- tmp
  }
  result
}

l <- list(a = 1, b = 2, c = 3)
enumerate(l, function(x, i) {
  cat("Name:  ", names(l)[[i]], "\n")
  cat("Value: ", x, "\n")
})