Re: [R] Log plus one transformation in R

2016-12-13 Thread John Sorkin
Duncan, Thank you. You are correct no one answered my question , despite the fact that several people reply to my email, until you replied. Your exclamation is quite clear and I thank you for your kindness. I did not pursue my question any further as I was concerned that I would be flamed. John

Re: [R] Log plus one transformation in R

2016-12-13 Thread Duncan Murdoch
On 12/12/2016 12:26 PM, John Sorkin wrote: David, I did read the help page. All it says is log1p(x) computes log(1+x) accurately also for |x| << 1 (and less accurately when x is approximately -1). This gives me pause. Does it mean that log(x) does not give accurate results? If log1p gives

Re: [R] Log plus one transformation in R

2016-12-12 Thread Faradj Koliev
Many thanks! logp1(x) worked just fine. Best, Faradj Skickat från min iPhone > 12 dec. 2016 kl. 22:54 skrev peter dalgaard : > > And, for crying out loud... just try it with x = 1.234e-16 or so. One would > think that the hint |x| << 1 was obvious enough. > > -pd > >> On

Re: [R] Log plus one transformation in R

2016-12-12 Thread peter dalgaard
And, for crying out loud... just try it with x = 1.234e-16 or so. One would think that the hint |x| << 1 was obvious enough. -pd > On 12 Dec 2016, at 18:26 , William Dunlap via R-help > wrote: > > Print more digits of the quotient or subtract one from it and you will

Re: [R] Log plus one transformation in R

2016-12-12 Thread Jeff Newmiller
Numerical accuracy in floating point math is a much broader discussion than R, but [1] seems to summarize it reasonably well. There are whole courses on this topic at university. [1] http://www.johndcook.com/blog/2010/06/07/math-library-functions-that-seem-unnecessary/ -- Sent from my phone.

Re: [R] Log plus one transformation in R

2016-12-12 Thread David Winsemius
> On Dec 12, 2016, at 9:26 AM, John Sorkin wrote: > > David, > > I did read the help page. All it says is > log1p(x) computes log(1+x) accurately also for |x| << 1 (and less accurately > when x is approximately -1). Not true. You evidently did not run the

Re: [R] Log plus one transformation in R

2016-12-12 Thread William Dunlap via R-help
The problem is that 1+x does not give accurate results for small x: > (1+1e-17) == 1 [1] TRUE Bill Dunlap TIBCO Software wdunlap tibco.com On Mon, Dec 12, 2016 at 9:26 AM, John Sorkin wrote: > David, > > I did read the help page. All it says is > > log1p(x)

Re: [R] Log plus one transformation in R

2016-12-12 Thread William Dunlap via R-help
Print more digits of the quotient or subtract one from it and you will see the difference: > log1p(0.01)/log(0.01+1) - 1 [1] 8.22666379463044e-11 Bill Dunlap TIBCO Software wdunlap tibco.com On Mon, Dec 12, 2016 at 8:53 AM, John Sorkin wrote: > At the

Re: [R] Log plus one transformation in R

2016-12-12 Thread John Sorkin
David, I did read the help page. All it says is log1p(x) computes log(1+x) accurately also for |x| << 1 (and less accurately when x is approximately -1). This gives me pause. Does it mean that log(x) does not give accurate results? If log1p gives more accurate values than log, why is the log

Re: [R] Log plus one transformation in R

2016-12-12 Thread David L Carlson
y 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

Re: [R] Log plus one transformation in R

2016-12-12 Thread David Winsemius
> On Dec 12, 2016, at 8:53 AM, John Sorkin 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(0.01)/log(0.01+1) > [1] 1 > John Read the help page

Re: [R] Log plus one transformation in R

2016-12-12 Thread John Sorkin
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(0.01)/log(0.01+1) [1] 1 John John David Sorkin M.D., Ph.D. Professor of Medicine Chief, Biostatistics and Informatics University of Maryland

Re: [R] Log plus one transformation in R

2016-12-12 Thread Martin Maechler
> Faradj Koliev > on Mon, 12 Dec 2016 17:23:20 +0100 writes: > Hi all, How do I perform log(x+1) in R? > log1p_trans() from the package ”scales" doesn’t seem to > work for me. amazing that you did not find log1p() in base R.

Re: [R] Log plus one transformation in R

2016-12-12 Thread William Dunlap via R-help
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] 9.95e-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,

Re: [R] Log plus one transformation in R

2016-12-12 Thread Spencer Graves
"?log" includes documentation for "log1p" in the base package Will that work? Spencer Graves On 12/12/2016 10:23 AM, Faradj Koliev 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

Re: [R] Log plus one transformation in R

2016-12-12 Thread John Sorkin
Faradj, I all you need to do is newvalue <- log(x+1) 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

[R] Log plus one transformation in R

2016-12-12 Thread Faradj Koliev
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