4 messages · Søren Højsgaard, Brian Ripley, Duncan Murdoch +1 more
Dear all, Given a number x<-1.234e12 is there a built-in function for extracting 1.234 and 12 ? The following "hack" seems clumpsy:
a<-strsplit(format(x, scientific=T),"e")[[1]] a
[1] "1.234" "+12"
as.numeric(a[1])
[1] 1.234
as.integer(a[2])
[1] 12 Regards S?ren
Dear all, Given a number x<-1.234e12 is there a built-in function for extracting 1.234 and 12 ?
No, because that is not how the number is stored (and in fact the value stored is a binary fraction with a slightly different value).
The following "hack" seems clumpsy:
format() is doing a lot of work to produce a decimal approximation to 'x', including choosing the precision. It is not clear what you want: if you merely want to express x as a*10^b for 1 <= a < 10 then b <- floor(log10(x)) a <- x/10^b does the job (but might get values of a very slightly less than 1 or above 10, so if you care this might need checking and refinement).
a<-strsplit(format(x, scientific=T),"e")[[1]] a
[1] "1.234" "+12"
as.numeric(a[1])
[1] 1.234
as.integer(a[2])
[1] 12 Regards S?ren
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
Dear all, Given a number x<-1.234e12 is there a built-in function for extracting 1.234 and 12 ?
I don't think so, but it is not hard to build them from log10:
mantissa <- function(x) {
if (x == 0) 0
else {
log <- log10(abs(x))
10^(log - floor(log))
}
}
exponent <- function(x) {
if (x == 0) 0
else floor(log10(abs(x)))
}
Duncan Murdoch
The following "hack" seems clumpsy:
a<-strsplit(format(x, scientific=T),"e")[[1]] a
[1] "1.234" "+12"
as.numeric(a[1])
[1] 1.234
as.integer(a[2])
[1] 12 Regards S?ren
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Hello,
Sorry I forgot to Cc the list.
And I had forgotten the case where x == 0.
extract <- function(x){
e <- ifelse(x == 0, 0, floor(log10(x)))
m <- x/10^e
list(mantissa = m, exponent = e)
}
extract(c(0, 1.234e12, 12345678901234, 123e123))
Hope this helps,
Rui Barradas
Em 23-06-2013 10:54, S?ren H?jsgaard escreveu:
Dear all, Given a number x<-1.234e12 is there a built-in function for extracting 1.234 and 12 ? The following "hack" seems clumpsy:
a<-strsplit(format(x, scientific=T),"e")[[1]] a
[1] "1.234" "+12"
as.numeric(a[1])
[1] 1.234
as.integer(a[2])
[1] 12 Regards S?ren
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.