I have encountered something about signif() that I don't understand.
It presents a problem for the situation in which I'm using it.
> foo <- 3.7e7
> formatC(foo,digits=22)
[1] " 37000000"> formatC(signif(foo,2),digits=22)
[1] "36999999.99999997764826"> formatC(signif(foo,3),digits=22)
[1] "36999999.99999997764826"> formatC(signif(foo,4),digits=22)
[1] "36999999.99999998509884"> formatC(signif(foo,5),digits=22)
[1] "36999999.99999999254942"> formatC(signif(foo,6),digits=22)
[1] "36999999.99999999254942"> formatC(signif(foo,7),digits=22)
[1] " 37000000"
The difference between foo and signif(foo,5) is large enough to make
a practical difference:
> signif(5.5e-7*foo,3)
[1] 20.4> signif(5.5e-7*signif(foo,5),3)
[1] 20.3
> round(5.5e-7*foo,1)
[1] 20.4> round(5.5e-7*signif(foo,5),1)
[1] 20.3
(foo is a unit conversion factor; I shouldn't need to use signif() on
it, but I was trying it as a workaround for another problem, and this
came up. 5.5e-7 is a measurement whose units need to be converted)
While I'm at it, why is this?> format(0.037,dig=22)
[1] "0.037"> formatC(0.037,dig=22)
[1] "0.03699999999999999816813"
> version
_
platform sparc-sun-solaris2.7
arch sparc
os solaris2.7
system sparc, solaris2.7
status
major 1
minor 6.2
year 2003
month 01
day 10
language R
Thanks
-Don
--
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Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
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