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-boun...@r-project.org] On Behalf Of John Sorkin Sent: Monday, December 12, 2016 10:54 AM To: farad...@gmail.com; r-help@r-project.org; wdun...@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@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 <farad...@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 > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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. Confidentiality Statement: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
