Unstructuring assignments in R...

unsass.R

###
### unsass.R
###
### a fairly syntactically clean way of doing unstructuring assignments in R
###
### syntax: (a~b~c) %=% list(A,B,C)
###
### not very tested
###
unsass <- function(lhs,rhs){
  nvalues = length(rhs)
  lhss = getFormulaNames(lhs)
  if(length(lhss)!=nvalues){
    stop("Wrong number of values to unpack")
  }

  for(i in 1:nvalues){
    eval(substitute(target <- value,
                    list(target=lhss[[i]],value=rhs[[i]])),
         envir=parent.frame())
  }
  invisible(0)
}

assign("%=%",unsass)

getFormulaNames <- function(formula){
  ## extract elements from a~b[1]~c~d
  ## recursive - might be an easier way...
  ##
  if(is.name(formula)){
    return(formula)
  }else{
    if(is.call(formula)){
      if(formula[[1]]=="~"){
        return(c(getFormulaNames(formula[[2]]),getFormulaNames(formula[[3]])))
      }else{
        return(formula)
      }
    }
  }
}

## samples
##
## #1 - the classic swapsie:
##
## > a=444
## > b=666
## > (a~b) %=% list(b,a)
## > a
## [1] 666
## > b
## [1] 444
##
## #2 - elemental, my dear watson:
## > a = 1:10
## > b = runif(4)
## > (a[4]~b[2]) %=% list(99,102)
## > a
##  [1]  1  2  3 99  5  6  7  8  9 10
## > b
## [1] 6.238385e-03 1.020000e+02 1.468159e-01 9.769772e-01
##
## #3 - several
## > a=1;b=2;c=3;d=4
## > (b~a~d~c) %=% list(a,b,c,d)
## > a
## [1] 2
## > b
## [1] 1
## > c
## [1] 4
## > d
## [1] 3