R help - Dec 2004 - Hexidecimal conversion

Help
I can produce the hexidecimal equivalent of a decimal number but I am having
a hard time reversing the operation. I'm good for hex representations to 159
and am close to extending to 2559. The archives are not clear on the
existence of a function for this task. Is there one?
Here is what I have got so far:
#Good for hex values to "9F"
as.decmode<-function(as.character(x)){
              hexDigit<-c(0:9,LETTERS[1:6])
              z<-matrix(c(strsplit(x, NULL),recursive=T),
              length(x),2,byrow=T)
              z.1<-as.numeric(z[,1])
              z.2<- match(z[,2],hexDigit)-1
              dec<-16*z.1+z.2
              return(dec)
              }
Alex Hanke
Department of Fisheries and Oceans
St. Andrews Biological Station
531 Brandy Cove Road
St. Andrews, NB
Canada
E5B 2L9



	[[alternative HTML version deleted]]

Some years ago I wrote a function to convert a number
from number system "base.in" to number system "base.out".
Here is the code:
<<*>>chcode <- function(b, base.in=2, base.out=10,
digits="0123456789ABCDEF"){
   # change of number systems, pw 10/02
   # e.g.: from 2 2 2 2 ...  ->  16 16 16 ...
   digits<-substring(digits,1:nchar(digits),1:nchar(digits))
   if(length(base.in)==1) base.in <- rep(base.in, max(nchar(b)-1))
   if(is.numeric(b)) b <- as.character(as.integer(b))
   b.num <- lapply(strsplit(b,""), function(x) match(x,digits)-1  )
   result <- lapply(b.num, function(x){
                cumprod(rev(c(base.in,1))[ 1:length(x) ] ) %*% rev(x)
             } )
   number<-unlist(result)
   cat("decimal representation:",number,"\n")

   if(length(base.out)==1){
      base.out<-rep(base.out,1+ceiling(log( max(number), base=base.out ) ) )
   }
   n.base <- length(base.out); result <- NULL
   for(i in n.base:1){
     result <- rbind(number %% base.out[i], result)
     number <- floor(number/base.out[i])
   }
   result[]<-digits[result+1]
   apply(result, 2, paste, collapse="")
}


@
... a short check:
<<*>>chcode("9F",16,10)

@
output-start
decimal representation: 159
[1] "0159"
output-end
@
... conversion backwards:
<<*>>chcode("159",10,16)

@
output-start
decimal representation: 159
[1] "09F"
output-end

Is chcode the function you are looking for?

Peter Wolf


Hanke, Alex wrote:
>Help
>I can produce the hexidecimal equivalent of a decimal number but I am having
>a hard time reversing the operation. I'm good for hex representations to
159
>and am close to extending to 2559. The archives are not clear on the
>existence of a function for this task. Is there one?
>Here is what I have got so far:
>#Good for hex values to "9F"
>as.decmode<-function(as.character(x)){
>              hexDigit<-c(0:9,LETTERS[1:6])
>              z<-matrix(c(strsplit(x, NULL),recursive=T),
>              length(x),2,byrow=T)
>              z.1<-as.numeric(z[,1])
>              z.2<- match(z[,2],hexDigit)-1
>              dec<-16*z.1+z.2
>              return(dec)
>              }
>Alex Hanke
>Department of Fisheries and Oceans
>St. Andrews Biological Station
>531 Brandy Cove Road
>St. Andrews, NB
>Canada
>E5B 2L9
>
>
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>  
>

Thanks to Patrick Burns, Peter Wolf and Duncan Murdoch who all provided me
with workable solutions to the hexidecimal conversion problem. They all work
and basically differ in the number of bells and whistles. 
Alex

-----Original Message-----
From: Duncan Murdoch [mailto:murdoch at stats.uwo.ca] 
Sent: December 2, 2004 9:42 AM
To: Hanke, Alex
Subject: Re: [R] Hexidecimal conversion


On Wed, 01 Dec 2004 15:07:16 -0400, "Hanke, Alex"
<HankeA at mar.dfo-mpo.gc.ca> wrote :
>
>Help
>I can produce the hexidecimal equivalent of a decimal number but I am
having
>a hard time reversing the operation. I'm good for hex representations to
159
>and am close to extending to 2559. The archives are not clear on the
>existence of a function for this task. Is there one?
I don't think so.
>Here is what I have got so far:
>#Good for hex values to "9F"
>as.decmode<-function(as.character(x)){
>              hexDigit<-c(0:9,LETTERS[1:6])
>              z<-matrix(c(strsplit(x, NULL),recursive=T),
>              length(x),2,byrow=T)
>              z.1<-as.numeric(z[,1])
>              z.2<- match(z[,2],hexDigit)-1
>              dec<-16*z.1+z.2
>              return(dec)
>              }
I think what you're missing is a loop over the characters.  You can
probably vectorize this to make it more efficient, but here's a
sketch:

hex2numeric <- function(x) {
    hexDigits <- c(0:9, LETTERS[1:6])
    chars <- strsplit(toupper(x), split=NULL)
    result <- rep(0, length(chars))
    for (i in seq(along=chars)) {
	for (j in seq(along=chars[[i]])) 
	    result[i] <- 16*result[i] + match(chars[[i]][j],
hexDigits) - 1
    }
    result
}

Duncan Murdoch

"Hanke, Alex" <HankeA at mar.dfo-mpo.gc.ca> wrote:
	I can produce the hex(a)decimal equivalent of a decimal number
	but I am having a hard time reversing the operation.

There are bound to be better ways, but perhaps the most obvious method
is
    (1) Break the string into single characters.
    (2) Match them up against the hexadecimal digits.
    (3) Multiply each digit by the appropriate power of 16.
    (4) Add 'em up.

hexdigits <-
c("0","1","2","3","4","5","6","7",
              
"8","9","A","B","C","D","E","F")

fromhex <- function (s) {
    s <- match(strsplit(s, "")[[1]], hexdigits) - 1
    sum(s * 16 ^ ((length(s)-1) : 0))
}