R/GrammarRandomExpression.R

In fnoorian/gramEvol: Grammatical Evolution for R

GrammarRandomExpression <- function(grammar, 
                                    numExpr = 1,
                                    max.depth = length(grammar$def), 
                                    startSymb = GrammarStartSymbol(grammar),
                                    max.string = GrammarMaxSequenceRange(grammar, max.depth, startSymb, approximate=TRUE),
                                    wrappings = 3,
                                    retries = 100) {
  n = length(max.string) # size of chromosome
  
  ret.list = list()
  for (i in 1:numExpr) {
    # repeat until a terminal grammar is found
    for (j in 1:retries) {
      # create a new genotype and phenotype
      genome = round(runif(n) * max.string)
      expr = GrammarGenotypeToPhenotype(genome, grammar, wrappings)
      
      # only pass it if is terminal
      if (expr$type == "T") {
        ret.list[[length(ret.list) + 1]] = parse(text=as.character(expr$parsed))
        break
      }
    }
    
    if (expr$type == "NT") {
      ret.list[[length(ret.list) + 1]] = NULL
    }
  }
  
  if (numExpr == 1)
    return (ret.list[[1]])
  else
    return (ret.list)
}