[R] Log plus one transformation in R

[William Dunlap]

Print more digits of the quotient or subtract one from it and you will see
the difference:

> log1p(0.000001)/log(0.000001+1) - 1
[1] 8.22666379463044e-11


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Dec 12, 2016 at 8:53 AM, John Sorkin <jsorkin at grecc.umaryland.edu>
wrote:

> At the risk of being flamed . . .
> What is the difference between log1p(x) and log(x+1)?
> The two methods appear to give the same results:
> > log1p(0.000001)/log(0.000001+1)
> [1] 1
> John
>
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
> Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
> >>> William Dunlap via R-help <r-help at r-project.org> 12/12/16 11:38 AM >>>
> log1p(x), in the base package computes log(1+x) accurately for small x (and
> large).
>
> E.g.,
> > options(digits=16)
> > base::log1p(1e-14)
> [1] 9.99999999999995e-15
> > base::log1p(1e-14) - base::log(1+1e-14)
> [1] 7.992778373591124e-18
> > as.numeric(log(Rmpfr::mpfr(1,precBits=1000) + Rmpfr::mpfr(1e-14,
> precBits=1000))) - log1p(1e-14)
> [1] 0
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Mon, Dec 12, 2016 at 8:23 AM, Faradj Koliev <faradj.g at gmail.com> wrote:
>
> > Hi all,
> >
> > How do I perform log(x+1) in R?
> >
> > log1p_trans() from the package ”scales" doesn’t seem to work for me.
> >
> > Best,
> > Faradj
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