vswitch

vswitch.R

vswitch <- function(namedList, default=NA, selector) {
  # Function adapted from Bill Dunlap that implements something along the lines of a vectorized switch statement.
  # http://tolstoy.newcastle.edu.au/R/e8/devel/09/12/1122.html
  #
  # Args:
  #    namedList - e.g., list(times=df$a * df$b, plus=df$a + df$b)
  #    default - a value to assign to elements of selector that aren't matched in namedList
  #    selector - e.g., c('times', 'times', 'plus', 'exp', 'plus')
  #
  # Returns: a vector of values selected from namedList
  #
  # Example:
  #  df <- data.frame(a=c(1,2,3,4,5), b=c(10, 9, 8, 7, 6))
  #  vswitch(namedList = list(times=df$a * df$b, plus=df$a + df$b),
  #          default = NA,
  #          selector = c('times', 'times', 'plus', 'exp', 'plus'))
  #  yields: 10 18 11 NA 11
  #
  ######################

  result <- rep(default, length.out=length(namedList[[1]]))
  for (sel in intersect(unique(selector[!is.na(selector)]), names(namedList))) {
      i <- sel == selector
      i[is.na(i)] <- FALSE
      result[i] <- namedList[[sel]][i]
  }
  result
}