R implementation of modelObject, modelSubObject and basic equation object OM

[rburghol]

Equation Evaluation

• evaluate() function uses "tryCatch"
• see also #1

    evaluate = function(){
      value <- tryCatch(
        {
          safe_envir <- c(self$data, self$arithmetic_operators)
          #value <-eval(parse(text=self$equation), envir=safe_envir)
          value <-eval(self$eq, envir=safe_envir)
        },
        error=function(cond) {
          # if no. of errors not exceeded,
          self$numnull <- self$numnull + 1
          if (self$numnull <= 5) {
            message(paste("Could not evaluate"))
            message(cond)
          }
          # Choose a return value in case of error
          value <- self$defaultvalue
        }
      )
      if (typeof(value) == 'closure') {
        # Choose a return value in case of error
        self$numnull <- self$numnull + 1
        if (self$numnull <= 5) {
          message(paste("Eval returned a function - check equation names for reserved words with undefined local values"))
          message(self$data)
        }
        value <- self$defaultvalue
      }
      return(value)
    }

References

• We used a technique that explicitly allows certain math functions, but needed some help to allow variable names, such as "release", which are also keywords -- OP here: https://stackoverflow.com/questions/18369913/safely-evaluating-arithmetic-expressions-in-r
• *pander - evals() https://stackoverflow.com/questions/1743698/evaluate-expression-given-as-a-string
• *substitute(expr,env) substitutes the expression with tokens found in env https://stat.ethz.ch/R-manual/R-devel/library/base/html/substitute.html

Objects

• Old version (deprecated): *S4 classes https://stat.ethz.ch/R-manual/R-devel/library/methods/html/Introduction.html
• New Version R6 classes.

[rburghol]

Advanced R expressions: http://adv-r.had.co.nz/Expressions.html