## Paul Johnson <pauljohn@ku.edu>
## 2012-01-30

## Special thanks to r-help email list contributors,
## especially Henrik Bengtsson.  Observe meaning of "parse"
## and eval.  parse creates an expression, from the "text"
## we type in. eval convertst that to results.

x1 <- "rgamma(10, shape = 3, scale = 2)"
class(x1)

## [1] "character"

eval(x1)

## [1] "rgamma(10, shape = 3, scale = 2)"

x1.parsed <- parse(text = x1)
class(x1.parsed)

## [1] "expression"

eval(x1.parsed)

##  [1]  3.977  1.795 13.321  2.818 15.881  2.977  4.446  5.706  4.424 11.829

## Get it? x1 is a character string we type in.
## parse converts that to a format that R understands.

## Now, embed a text character variable inside a matrix
## that is filled with character strings..

BM <- matrix("0.1", 5, 5)

BM[2,1] <- "a"
BM[3,2] <- "b"

BM

##      [,1]  [,2]  [,3]  [,4]  [,5] 
## [1,] "0.1" "0.1" "0.1" "0.1" "0.1"
## [2,] "a"   "0.1" "0.1" "0.1" "0.1"
## [3,] "0.1" "b"   "0.1" "0.1" "0.1"
## [4,] "0.1" "0.1" "0.1" "0.1" "0.1"
## [5,] "0.1" "0.1" "0.1" "0.1" "0.1"

parseAndEval <- function(x, ...) eval(parse(text=x))

a <- 0.5
b <- 0.4

realBM <- apply(BM, MARGIN=c(1,2), FUN=parseAndEval)

BM[4,5] <- "rnorm(1, m=7, sd=1)"

BM

##      [,1]  [,2]  [,3]  [,4]  [,5]                 
## [1,] "0.1" "0.1" "0.1" "0.1" "0.1"                
## [2,] "a"   "0.1" "0.1" "0.1" "0.1"                
## [3,] "0.1" "b"   "0.1" "0.1" "0.1"                
## [4,] "0.1" "0.1" "0.1" "0.1" "rnorm(1, m=7, sd=1)"
## [5,] "0.1" "0.1" "0.1" "0.1" "0.1"

realBM <- apply(BM, MARGIN=c(1,2), FUN=parseAndEval)

realBM

##      [,1] [,2] [,3] [,4]  [,5]
## [1,]  0.1  0.1  0.1  0.1 0.100
## [2,]  0.5  0.1  0.1  0.1 0.100
## [3,]  0.1  0.4  0.1  0.1 0.100
## [4,]  0.1  0.1  0.1  0.1 7.244
## [5,]  0.1  0.1  0.1  0.1 0.100

## Now, what about gui interaction with that table?
## The best "nice looking" options are not practical at the moment.

## Try this instead

data.entry(BM)

## That will work on all platforms, so far as I know, without
## any special effort from us.     Run that, make some changes, then
## make sure you insert new R variables to match in your environment.

## Suppose you inserted the letter z in there somewhere. Go do that.

BM[1,1] <- "z"

BM

##      var1  var2  var3  var4  var5                 
## [1,] "z"   "0.1" "0.1" "0.1" "0.1"                
## [2,] "a"   "0.1" "0.1" "0.1" "0.1"                
## [3,] "0.1" "b"   "0.1" "0.1" "0.1"                
## [4,] "0.1" "0.1" "0.1" "0.1" "rnorm(1, m=7, sd=1)"
## [5,] "0.1" "0.1" "0.1" "0.1" "0.1"

## z's just a letter in the character matrix. It is not defined yet.

## set z out here

z <- rpois(1, lambda=10)


realBM <- apply(BM, MARGIN=c(1,2), FUN=parseAndEval)
realBM

##      var1 var2 var3 var4  var5
## [1,]  9.0  0.1  0.1  0.1 0.100
## [2,]  0.5  0.1  0.1  0.1 0.100
## [3,]  0.1  0.4  0.1  0.1 0.100
## [4,]  0.1  0.1  0.1  0.1 5.545
## [5,]  0.1  0.1  0.1  0.1 0.100