[R] Log plus one transformation in R

[David L Carlson]

The difference increases as the value gets closer to 0:

> dput(log1p(0.000001))
9.99999500000333e-07
> dput(log(1+0.000001))
9.99999499918067e-07

> dput(log1p(0.000001)/log(0.000001+1))
1.00000000008227
> dput(log1p(0.00000001)/log(0.00000001+1))
1.00000000607747
> dput(log1p(0.0000000001)/log(0.0000000001+1))
0.999999917259636
> dput(log1p(0.000000000001)/log(0.000000000001+1))
0.99991110732027
> dput(log1p(0.00000000000001)/log(0.00000000000001+1))
1.00079991719344

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of John Sorkin
Sent: Monday, December 12, 2016 10:54 AM
To: faradj.g at gmail.com; r-help at r-project.org; wdunlap at tibco.com
Subject: Re: [R] Log plus one transformation in R

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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