[R] Obtain the hex code for a given character.

[Duncan Murdoch]

On 14-02-04 7:57 PM, Rolf Turner wrote:
>
>
> If I have a character such as "£" stored in a object called "xxx", how
> can I obtain the hex code representation of this character?  In this
> case I know that the hex code is "\u00A3", but if I didn't, how would I
> find out?

charToRaw will give you the bytes used to store it:

 > charToRaw("£")
[1] c2 a3

That was on MacOS, which uses UTF-8 encoding.  On Windows, using Latin1,

 > charToRaw("£")
[1] a3

You won't see 00A3, because that's not an encoding that R uses, that's 
the Unicode "code point".  It's not too hard to get to that from the 
UTF-8 encoding, but I don't know any R function that does it.

>
> I would like a function "foo()" such that foo(xxx) would return, say,
> the string "00A3".

I don't know how to get that string, but as.character(charToRaw(x)) will 
put the bytes for x in strings, e.g.

as.character(charToRaw("£"))

gives

[1] "c2" "a3"

on a Mac.

>
> I have googled and otherwise searched around and have come up with
> nothing that seemed at all helpful to me.  If I am missing something
> obvious, please point me at it.
>
> (I have found a table on the web, which contains the information that I
> need, but it is only accessible "by eye" as far as I can discern.)
>
> Supplementary question:  Suppose I have the string "00A3" stored in
> an object called "yyy".  How do I put that string together with "\u"
> so as to obtain "£"?  I thought I could do
>
> 	xxx <- paste("\u",yyy,sep="")
>
> but R won't let me use "\u" "without hex digits".  How can I get around
> this?

The \u notation with a code point is handled by the R parser, so you 
need to parse that string, which means putting it in quotes first, e.g.

xxx <- eval(parse(text = paste0("'\\u", yyy, "'")))

That seems pretty excessive.  You'd probably be better off doing all of 
this in C instead...

Duncan Murdoch

>
> Thanks.
>
> cheers,
>
> Rolf Turner
>
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