R help - May 2005 - Chars as numbers

Is there a proper function for transforming
a character to a number instead of using

   i=match('c',letters)
   # 3

Thanks.
Josef Eschgf??ller

-- 
Josef Eschgf??ller
Dipartimento Matematico
Universita' di Ferrara
http://felix.unife.it

Josef,

Not sure if this is exactly what you mean, but there is a generic function

as()

to which you can then specify "numeric" as an argument and which then 
coerces stuff into numeric format.

Tobias


Josef Eschgfaeller wrote:
> 
> Is there a proper function for transforming
> a character to a number instead of using
> 
>   i=match('c',letters)
>   # 3
> 
> Thanks.
> Josef Eschgf??ller
> 
> 
> ------------------------------------------------------------------------
> 
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> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
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**************************************************************************
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"I never failed once. I invented the light bulb.
It just happened to be a 2000-step process."

as.numeric()
hih

Josef Eschgfaeller wrote:
> 
> Is there a proper function for transforming
> a character to a number instead of using
> 
>   i=match('c',letters)
>   # 3
I'd suggest to use the above if you really mean it. Note that 
"transforming a character to a number" is not well defined, because
you
have to think about encodings and characters at first. See the article 
by Brian Ripley in the most recent issue of R News, for example.

Uwe Ligges

> Thanks.
> Josef Eschgf??ller
> 
> 
> ------------------------------------------------------------------------
> 
> ______________________________________________
> 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

> as.numeric
Some weeks ago one discussed on the list about how
to transform a hexadecimal representation to
decimal digits. Specifically one has to transform
'a' to 10 etc. In C one does this with 'a'-87,
but I did not find a function for this in R.
Using match on letterdigits as in the following
is of course a little slow when repeated often.
---------------------------------------
Hex = function (rep16)
{rep16=tolower(rep16)
u=strsplit(rep16,'',perl=T)[[1]]
letterdigits=c(0:9,letters)
v=sapply(u,function (x)
   match(x,letterdigits)-1)
v=as.numeric(v)
Horner(v,16)}

Horner = function (v,alfa=2)
{b=v[1]; m=length(v)
if (m>1) for (i in 2:m)
b=b*alfa+v[i]; b}

# Example:
for (x in c('0','a0','10e','f0ae'))
print(Hex(x))
# 0
# 160
# 270
# 61614
---------------------------------------
Josef Eschgf??ller

-- 
Josef Eschgf??ller
Dipartimento Matematico
Universita' di Ferrara
http://felix.unife.it