Troels, this is due to the usual tiny difference between numbers as computed by R and the numbers that you think they are!
tt <- seq(0,20,by=0.02) dtt <- diff(tt) length(dtt) # [1] 1000 r02 <- rep(0.02,1000) unique(r02 - dtt) # [1] 0.000000e+00 3.469447e-18 -3.469447e-18 1.040834e-17 # [5] -1.734723e-17 3.816392e-17 9.367507e-17 2.046974e-16 # [9] 4.267420e-16 -4.614364e-16 -1.349615e-15 -3.125972e-15 Hoping this helps! Ted. On 11-Jan-2015 08:29:26 Troels Ring wrote: > R version 3.1.1 (2014-07-10) -- "Sock it to Me" > Copyright (C) 2014 The R Foundation for Statistical Computing > Platform: x86_64-w64-mingw32/x64 (64-bit) > > Dear friends - I have a small problem with diff (I guess) > I made a sequence with fixed interval between consecutive elements - and > hence thought the diff would be as specified > but had a vector with apparently identical 12 elements returned from diff > tt <- seq(0,20,by=0.02) > unique(diff(tt)) #[1] 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 > 0.02 0.02 > Trying to see if these elements in diff were duplicated > duplicated(diff(tt)) >#[1] FALSE TRUE FALSE FALSE TRUE FALSE FALSE TRUE TRUE and from > sum(duplicated(diff(tt))) > [1] 988 > saw that 12 of the elements in duplicated(diff(tt)) were FALSE. Would it > be expected that the first was FALSE and the rest TRUE? >|duplicated()|determines which elements of a vector or data frame are > duplicates of elements with smaller subscripts, and returns a logical > vector indicating which elements (rows) are duplicates. > > All best wishes > Troels > Aalborg, Denmark > > [[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. ------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@wlandres.net> Date: 11-Jan-2015 Time: 08:48:03 This message was sent by XFMail ______________________________________________ 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.
