Colleagues
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System info:
Version 1.2.3 (2001-04-26) on NT
ESS v. 5.1.18 using emacs ver. 20.4
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I am wondering if there is a problem with the function rep(). Both the
commands using rep() below were expected to produce 8 twos, but only
the second did.
x <- rep(2,40*(1-0.8))
length(x)
y <- rep(2,40*0.2)
length(y)
Have I misused the function? Should the second argument of rep() be
limited to a single number or a vector of the same length as the first
argument as it documents in the help? Or is this a bug?
Help will be appreciated.
Thanks
Sam
Sam McClatchie, Research scientist (fisheries acoustics))))))))))
NIWA (National Institute of Water & Atmospheric Research Ltd)
PO Box 14 901, Kilbirnie, Wellington, New Zealand
s.mcclatchie at niwa.cri.nz
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"S.McClatchie" wrote:> > Colleagues > > ---------------------------------- > System info: > Version 1.2.3 (2001-04-26) on NT > ESS v. 5.1.18 using emacs ver. 20.4 > > ---------------------------------- > I am wondering if there is a problem with the function rep(). Both the > commands using rep() below were expected to produce 8 twos, but only > the second did. > > x <- rep(2,40*(1-0.8)) > length(x) > > y <- rep(2,40*0.2) > length(y) > > Have I misused the function? Should the second argument of rep() be > limited to a single number or a vector of the same length as the first > argument as it documents in the help? Or is this a bug? > > Help will be appreciated. > ThanksThis happens because of computational (un)exactness: (1-0.8) == 0.2 [1] FALSE options(digits=22) 1-0.8 [1] 0.19999999999999996 0.2 [1] 0.2 And because in this case R interprets (1-0.8) < 0.2, also floor(40*(1*0.8)) is 7. ;-) Uwe Ligges -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Sam McClatchie wrote:>I am wondering if there is a problem with the function rep(). Both the >commands using rep() below were expected to produce 8 twos, but only >the second did.>x <- rep(2,40*(1-0.8)) >length(x)>y <- rep(2,40*0.2) >length(y)>Have I misused the function? Should the second argument of rep() be >limited to a single number or a vector of the same length as the first >argument as it documents in the help? Or is this a bug?This sounds to me like a rounding problem. Recall that a computer always has a limited precision in its calculations (except when using infinite precision algorithms like in Mathematica) and it could sometimes produce unexpected results. As an evidence of that, z <- rep(2, 40*(1-0.79999999999999)) produces 8 twos, as expected. With other value, behavior of rep() is "correct": rep(2, 40*0.4) and rep(2, 40*(1-0.6)) both give 16 twos, as expected. Best regards, Philippe ...........]<(({?<...............<?}))><............................... ) ) ) ) ) __ __ ( ( ( ( ( |__) | _ ) ) ) ) ) | hilippe |__)rosjean ( ( ( ( ( Marine Biol. Lab., ULB, Belgium ) ) ) ) ) __ ( ( ( ( ( |\ /| |__) ) ) ) ) ) | \/ |ariculture & |__)iostatistics ( ( ( ( ( ) ) ) ) ) e-mail: phgrosje at ulb.ac.be or phgrosjean at sciviews.org ( ( ( ( ( SciViews project coordinator (http://www.sciviews.org) ) ) ) ) ) tel: 00-32-2-650.29.70 (lab), 00-32-2-673.31.33 (home) ( ( ( ( ( ) ) ) ) ) "I'm 100% confident that p is between 0 and 1" ( ( ( ( ( L. Gonick & W. Smith (1993) ) ) ) ) ) ....................................................................... -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._