[R] 1 not equal to 1, and rep command
sarah.goslee at gmail.com
Mon Sep 12 18:46:04 CEST 2011
Not so strange, in fact this is FAQ 7.31, and has to do (as you guess)
with the way that computers store numbers.
You need to do as you did, and use round() or floor() or similar to
ensure that you get the results you expect.
2011/9/12 Benjamin Høyer <bdhoyer at gmail.com>:
> I need to use rep() to get a vector out, but I have spotted something very
> strange. See the reproducible example below.
> N <- 79
> seg <- 5
> segN <- N / seg # = 15.8
> d1 <- seg - ( segN - floor(segN) ) * seg
> d1 # = 1
> rep(2, d1) # = numeric(0), strange - why doesn't it print one "2"?
> rep(2, 1) # 2, ok
> rep(2, d1 / 1,1) # 2, this does work
> rep(2, d1 + 2) # "2 2" - also works but...
> d1 + 2 # = 3! so why does it print two 2s above?
> d1 == 1 # FALSE
> all.equal(d1, 1) # TRUE
> identical(d1, 1) # FALSE
> Try something else...
> d2 <- 4 - ( (79/4) - floor(79/4))* 4
> d2 # = 1
> rep(2, d2) # 2 : this works!
> d2 == 1 # TRUE
> all.equal(d2, 1) # TRUE
> identical(d2, 1) # TRUE
> #version info
> platform x86_64-pc-linux-gnu
> arch x86_64
> os linux-gnu
> system x86_64, linux-gnu
> major 2
> minor 10.1
> year 2009
> month 12
> day 14
> svn rev 50720
> language R
> version.string R version 2.10.1 (2009-12-14)
> Seems like there's some binary maths errors here somewhere. Very strange to
> me. Anyway, I need to be able to use the result d1 in a rep() command. Any
> way to force rep not to be *too* specific in how it reads its "times"
> Thanks in advance,
> Benjamin Hoyer
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