buildFormulaWithTrendAndSeason.R

buildFormula <- function(dataset, LTerms, useTrend=FALSE, useSeason=FALSE) {
  
  lLen <- length(LTerms)
  
  for (i in 1:lLen)
    assign(paste("fact", i, sep=""), L(dataset, LTerms[i]))
  
  factors = array()
  for (i in 1:lLen)
    factors[i] <- paste("fact",  i , sep="")
  
  formTerms <- paste("dataset ~ ")
  if (useTrend) {
    trendFactor <- trend(dataset)
    factors <- c("trendFactor", factors)
  }
  
  if (useSeason) {
    seasonFactor <- season(dataset)
    factors <- c("seasonFactor", factors)
  }
  
  form = as.formula(paste(formTerms, paste(factors, collapse="+")))
  return(form)
}

#call example
form <- buildFormula(sales_aggr, c(1,6,12), useTrend=TRUE)