Matthew, I see. I din't think about tolerance. Although dt[with(dt, order(y)), ]
seems to do the task right (similar to data.frame). I'm glad that I don't have to convert to data.frame to perform the order. I am not keying by this column. Unless one needs this column for keying, I don't think a tolerance option is essential. Although, having it definitely would be only nicer. Arun On Tuesday, April 30, 2013 at 4:09 PM, Matthew Dowle wrote: > > Hi, > data.table sorts double within machine tolerance : > > sqrt(.Machine$double.eps) > [1] 1.490116e-08 > > > > i.e. numbers closer than this are considered equal. > > Otherwise we wouldn't be able to do things like DT[.(3.14)]. > > I had a quick look, see arguments of data.table:::ordernumtol which takes > "tol" but there is no option provided (yet) to change this. Do we need one? > > In the examples section of one of the help pages it has an example which > generates a series of numers very close together using pi. Note that your > numbers are both close together, and, very close to 0. > > Matthew > > On 30.04.2013 14:52, Arunkumar Srinivasan wrote: > > Hi there, > > I just saw something strange when I was sorting a column of p-values. I > > checked the data.table bug tracker for words "sort" and "floating point" > > and there were no hits for this case. There's a bug for "integer 64" sort > > on a column though. > > So, here's a reproducible example. I'd be glad to file a bug, if it is and > > be corrected if it's something I am doing wrong. > > set.seed(45) > > dt <- data.table(x=sample(50), y= sample(c(seq(0, 1, length.out=1000), > > 7000000:7000100), 50)/1e7) > > head(dt) > > x y > > 1: 32 5.395395e-08 > > 2: 16 6.956957e-08 > > 3: 12 2.142142e-08 > > 4: 18 5.855856e-08 > > 5: 17 6.216216e-08 > > 6: 14 5.025025e-08 > > setkey(dt, "y") # sort by column y > > head(dt, 10) > > x y > > 1: 47 1.401401e-09 > > 2: 12 2.142142e-08 > > 3: 24 1.391391e-08 > > 4: 43 9.809810e-09 <~~~ obviously false > > 5: 1 2.932933e-08 > > 6: 48 2.562563e-08 > > 7: 49 1.891892e-08 > > 8: 40 2.182182e-08 > > 9: 9 7.307307e-09 <~~~ obviously false > > 10: 45 2.482482e-08 > > > > Best, > > Arun > > > > > > > > >
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