Ranadu: Functions for use with RAF aircraft data files

# load the csym data.frame containing symbols and definitions
# load (file=paste (find.package ("Ranadu"), "Constants.txt", sep='/'))
# CHANGE: csym is now saved in R/sysdata.rda

#' @title StandardConstant
#' @description Provides standard values of constants as used in the Processing Algorithms 
#' document, and others.
#' @details If one of the standard symbol names is provided, the routine returns the value 
#' associated with that constant. Otherwise, it returns NULL. For special cases described 
#' following the parameter Symbol, the returned value is a list of available symbols or an 
#' expanded explanation of a specified symbol.
#' @aliases standardConstant
#' @author William Cooper
#' @export StandardConstant
#' @param Symbol One of a set of defined symbols. To see the available symbols, 
#' use StandardConstant('?'), and to see a full description of an available symbol, 
#' use for example StandardConstant("?Rd").
#' @return The value associated with that symbol.
#' @examples 
#' StandardConstant ("MWW")
StandardConstant <- function (Symbol) {
  if (!exists ("csym")) {load(file="R/sysdata.rda")}
  if (Symbol == '?') {
    return (row.names (csym))
  }
  if(substring (Symbol, 1, 1) == '?') {
    return (csym[substring (Symbol, 2, nchar(Symbol)), ])
  }
  return(csym[Symbol,1])
}

# # here is one way to construct and add to the data.frame 
# # containing the symbol references, values, and explanations:
# csym <- data.frame (c(9.80665,273.15,8.314472e3), row.names=c("g_standard", "Tzero", "Ru"))
# csym <- cbind (csym, data.frame(c("m/s","K","J/(kmol K)")))
# csym <- cbind (csym, data.frame (c("standard-atmosphere acceleration of gravity","T in kelvin corresponding to 0 C", "universal gas constant")))
# colnames(csym) <- c("value","units","description")
# ca <- data.frame ("MWW"=18.0153, row.names="MWW")
# ca[2] <- "kg/kmol"
# ca[3] <- "molecular weight of water"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("MWD"=28.9637, row.names="MWD")
# ca[2] <- "kg/kmol"
# ca[3] <- "molecular weight, weighted average for dry air"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("T3W"=273.16, row.names="T3W")
# ca[2] <- "K"
# ca[3] <- "triple point temperature of water"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Na"=6.022141e26, row.names="Na")
# ca[2] <- "molecules/kmol"
# ca[3] <- "Avogadro constant"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("kB"=csym["Ru",1]/csym["Na",1], row.names="kB")
# ca[2] <- "J/K"
# ca[3] <- "Boltzman constant"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Rd"=csym["Ru",1]/csym["MWD",1], row.names="Rd")
# ca[2] <- "J/(kg K)"
# ca[3] <- "gas constant for dry air"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Rw"=csym["Ru",1]/csym["MWW",1], row.names="Rw")
# ca[2] <- "J/(kg K)"
# ca[3] <- "gas constant for water vapor"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Re"=6.371229e6, row.names="Re")
# ca[2] <- "m"
# ca[3] <- "radius of the Earth (as used by INUs)"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("cpd"=3.5*csym["Rd",1], row.names="cpd")
# ca[2] <- "J/(kg K)"
# ca[3] <- "specific heat of dry air at constant pressure"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("cvd"=2.5*csym["Rd",1], row.names="cvd")
# ca[2] <- "J/(kg K)"
# ca[3] <- "specific heat of dry air at constant volume"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("gamma"=csym["cpd",1]/csym["cvd",1], row.names="gamma")
# ca[2] <- "dimensionless"
# ca[3] <- "ratio of specific heats for dry air, cpd/cpv"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Omega"=7.292115e-5, row.names="Omega")
# ca[2] <- "radians/s"
# ca[3] <- "angular rotation rate of the Earth"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("OmegaSch"=sqrt(csym["g_standard",1]/csym["Re",1]), row.names="OmegaSch")
# ca[2] <- "radians/s"
# ca[3] <- "angular frequency of the Schuler oscillation"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("sigmaSB"=5.6704e-8, row.names="sigmaSB")
# ca[2] <- "W/(m^2 K^4)"
# ca[3] <- "Stephan-Boltzmann Constant"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Cradeg"=pi/180., row.names="Cradeg")
# ca[2] <- "radians/degree"
# ca[3] <- "conversion to radians from degrees"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Cmeterft"=0.3048, row.names="Cmeterft")
# ca[2] <- "m/ft"
# ca[3] <- "conversion to meters from feet"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Cmfromnmi"=1852., row.names="Cmfromnmi")
# ca[2] <- "meters/(n mi)"
# ca[3] <- "conversion to meters from n mi"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)
# ca <- data.frame ("Cktmps"=csym["Cmfromnmi",1]/3600., row.names="Cktmps")
# ca[2] <- "knots/(m/s)"
# ca[3] <- "conversion to m/s from knots"
# colnames(ca) <- colnames(csym)
# csym <- rbind (csym, ca)

# here is a model for how to do this faster, if that becomes an issue:
### get dataset
# #load(url("http://dl.dropbox.com/u/61803503/NETtalk.RData"))
# load ("/home/cooperw/Downloads/NETtalk.RData")
# ### set up data.table
# 
# library(data.table)
# library(microbenchmark)
# 
# hash <- function(x) {e <- new.env(hash = TRUE, size = nrow(x),       
#                                   parent = emptyenv()); apply(x, 1, function(col) assign(col[1],     
#                                                                                          as.numeric(col[2]), envir = e)); return(e)}  
# 
# env <- hash(NETtalk)  #assign the dictionary to env
# 
# # NETtalk.table <- data.table(NETtalk, key="word")
# # vectorScan <- function()NETtalk[NETtalk$word=="stuff",]
# # dataTable <- function() NETtalk.table[J("stuff"),]
# hash <- function() get("stuff", e = env)
# 
# (op <- microbenchmark( 
#   #   vectorScan(),
#   #   dataTable(),
#   hash(),        
#   times=1000L))