R Functions

How it works

A function groups an operation behind named arguments. R returns the last evaluated expression unless return is used explicitly. Validate the inputs before a calculation that assumes a particular type or shape. This function accepts a small non-empty numeric vector of whole non-negative visit counts and computes its total.

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Example

local({
  previous_options <- options(warn = 2, digits = 8, stringsAsFactors = FALSE)
  on.exit(options(previous_options), add = TRUE)
  check_counts <- function(x, allow_missing = FALSE, allow_empty = FALSE) {
    if (!(is.integer(x) || is.double(x)) || is.object(x) || !is.null(dim(x))) {
      stop("Use a plain numeric vector")
    }
    if (length(x) > 256L || (!allow_empty && length(x) == 0L)) {
      stop("Use 1..256 counts unless empty input is explicitly allowed")
    }
    if (any(is.nan(x)) || (!allow_missing && anyNA(x))) {
      stop("Missing or undefined counts are not allowed here")
    }
    observed <- x[!is.na(x)]
    if (any(!is.finite(observed)) || any(observed < 0) ||
        any(observed > 1000000) || any(observed != floor(observed))) {
      stop("Counts must be finite whole numbers from 0 to 1000000")
    }
    invisible(x)
  }

  total_visits <- function(visits) {
    check_counts(visits)
    sum(visits)
  }
  cat("total:", total_visits(c(8, 12, 10)), "\n")
  invisible(NULL)
})

check_counts <- function(x, allow_missing = FALSE, allow_empty = FALSE) {
  if (!(is.integer(x) || is.double(x)) || is.object(x) || !is.null(dim(x))) {
    stop("Use a plain numeric vector")
  }
  if (length(x) > 256L || (!allow_empty && length(x) == 0L)) {
    stop("Use 1..256 counts unless empty input is explicitly allowed")
  }
  if (any(is.nan(x)) || (!allow_missing && anyNA(x))) {
    stop("Missing or undefined counts are not allowed here")
  }
  observed <- x[!is.na(x)]
  if (any(!is.finite(observed)) || any(observed < 0) ||
      any(observed > 1000000) || any(observed != floor(observed))) {
    stop("Counts must be finite whole numbers from 0 to 1000000")
  }
  invisible(x)
}

total_visits <- function(visits) {
  check_counts(visits)
  sum(visits)
}
cat("total:", total_visits(c(8, 12, 10)), "\n")

Expected result

total: 30

The validator rejects logical values, factors, matrices, missing values and unsupported ranges rather than relying on accidental coercion. Its size limits are specific to this teaching function, not limits on R itself. A later project opts into a distinct missing-value policy deliberately.