Skip to content

Unexpected output from round()

3 messages · Dennis Fisher, John Maindonald, Duncan Murdoch

Original
Dennis Fisher
# 
R 3.2.0
OS X

Colleagues

I received unexpected output from a command issued in a terminal window:
c(82.9888290534313, 100.544763749464)
c(82.9888290534313, 100.544763749464)
[1]  82.98999999999999 100.54000000000001

I expected the result of the second command to be:
	82.99   100.54

Interesting, the problem also occurs if I round to 5 or 8 digits.  

Of note, the problem does NOT occur in R GUI or in Windows.

I am aware of FAQ 7.31 (Why doesn?t R think these numbers are equal?) but I don?t see how this could be manifestation of that issue.

I am curious as to the explanation of this issue.

Dennis


Dennis Fisher MD
P < (The "P Less Than" Company)
Phone: 1-866-PLessThan (1-866-753-7784)
Fax: 1-866-PLessThan (1-866-753-7784)
www.PLessThan.com
John Maindonald
# 
I cannot reproduce it (R version 3.2.0 Patched (2015-04-19 r68206)) in a terminal window:
3.14159265358979
3.14159265358979
[1] 3.14
c(82.9888290534313, 100.544763749464)
c(82.9888290534313, 100.544763749464)
[1]  82.99 100.54
R version 3.2.0 Patched (2015-04-19 r68206)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X 10.10.3 (Yosemite)

locale:
[1] en_NZ.UTF-8/en_NZ.UTF-8/en_NZ.UTF-8/C/en_NZ.UTF-8/en_NZ.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base  

John Maindonald             email: john.maindonald at anu.edu.au
Duncan Murdoch
#
On 12/06/2015 8:53 PM, John Maindonald wrote:
If you set options(digits=16) you'll get it.  It's just FAQ 7.31, and
the fact that R only stores 15 or 16 digit accuracy.

Duncan Murdoch