[R] cut{base}: is it a bug?

[Jeff Newmiller]

"Subtracting a bit" only fixes the problem for the test data... it introduces a bias in any continuous data you happen to throw at it. However, if you have data with known rounding applied (e.g. published tabular data) then the subtracting trick can be useful. In general you should not expect floating point fractions to behave like exact values in your analysis.

On September 24, 2018 8:14:09 AM PDT, David L Carlson <dcarlson using tamu.edu> wrote:
>You've been bitten by FAQ 7.31: Why doesn't R think these numbers are
>equal?
>https://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f
>
>Your boundaries and your data values are not what you think they are.
>This is a limitation of digital computing not R.
>
>> print(seq(from=.6, to=2.2, by=.2), digits=17)
>[1] 0.59999999999999998 0.80000000000000004 1.00000000000000000
>1.20000000000000018
>[5] 1.39999999999999991 1.60000000000000009 1.80000000000000027
>2.00000000000000000
>[9] 2.20000000000000018
>
>> print(dat, digits=17)
>[1] 0.59999999999999998 0.59999999999999998 0.59999999999999998
>0.69999999999999996
>[5] 0.69999999999999996 0.69999999999999996 0.69999999999999996
>0.69999999999999996
>[9] 0.80000000000000004 0.80000000000000004 0.80000000000000004
>0.90000000000000002
>[13] 0.90000000000000002 0.90000000000000002 0.90000000000000002
>1.00000000000000000
>[17] 1.00000000000000000 1.00000000000000000 1.00000000000000000
>1.10000000000000009
>[21] 1.10000000000000009 1.10000000000000009 1.19999999999999996
>1.19999999999999996
>[25] 1.19999999999999996 1.19999999999999996 1.30000000000000004
>1.30000000000000004
>[29] 1.30000000000000004 1.39999999999999991 1.39999999999999991
>1.39999999999999991
>[33] 1.50000000000000000 1.50000000000000000 1.50000000000000000
>1.60000000000000009
>[37] 1.60000000000000009 1.69999999999999996 1.69999999999999996
>1.69999999999999996
>[41] 1.69999999999999996 1.80000000000000004 1.80000000000000004
>1.80000000000000004
>[45] 1.89999999999999991 1.89999999999999991 2.00000000000000000
>2.00000000000000000
>[49] 2.00000000000000000 2.00000000000000000 2.00000000000000000
>2.10000000000000009
>
>The simplest solution is to subtract a bit. This also means you don't
>need the include.lowest= or right= arguments:
>
>> f <- cut(dat,
>+           breaks= seq(from=.6-.01, to=2.2-.01, by=.2),
>+           dig.lab=10L)
>> as.matrix(tb <- table(f))
>            [,1]
>[0.59,0.79)    8
>[0.79,0.99)    7
>[0.99,1.19)    7
>[1.19,1.39)    7
>[1.39,1.59)    6
>[1.59,1.79)    6
>[1.79,1.99)    5
>[1.99,2.19]    6
>
>----------------------------------------
>David L Carlson
>Department of Anthropology
>Texas A&M University
>College Station, TX 77843-4352
>
>
>-----Original Message-----
>From: R-help <r-help-bounces using r-project.org> On Behalf Of Jose Claudio
>Faria
>Sent: Monday, September 24, 2018 9:32 AM
>To: r-help using r-project.org
>Subject: [R] cut{base}: is it a bug?
>
>Dears members,
>
>Is the below a bug of the cut {base} function?
>
>dat <- c(
> 0.6, 0.6, 0.6, 0.7, 0.7, 0.7, 0.7, 0.7, #(8)
> 0.8, 0.8, 0.8, 0.9, 0.9, 0.9, 0.9,        #(7)
> 1.0, 1.0, 1.0, 1.0, 1.1, 1.1, 1.1,        #(7)
> 1.2, 1.2, 1.2, 1.2, 1.3, 1.3, 1.3,        #(7)
> 1.4, 1.4, 1.4, 1.5, 1.5, 1.5,               #(6)
> 1.6, 1.6, 1.7, 1.7, 1.7, 1.7,               #(6)
> 1.8, 1.8, 1.8, 1.9, 1.9,                      #(5)
> 2.0, 2.0, 2.0, 2.0, 2.0, 2.1                #(6)
> )
>
># making class from function "cut"
>(f <- cut(dat,
>          breaks= seq(from=.6, to=2.2, by=.2),
>          include.lowest=TRUE,
>          dig.lab=10L,
>          right=FALSE))
>
># more easy to see the table
>as.matrix(tb <- table(f))
>
># Checking
>print(length(dat[dat >= 0.6 & dat < 0.8])) == tb[1]
>print(length(dat[dat >= 0.8 & dat < 1.0])) == tb[2]
>print(length(dat[dat >= 1.0 & dat < 1.2])) == tb[3]  # !?
>print(length(dat[dat >= 1.2 & dat < 1.4])) == tb[4]  # !?
>print(length(dat[dat >= 1.4 & dat < 1.6])) == tb[5]
>print(length(dat[dat >= 1.6 & dat < 1.8])) == tb[6]  # !?
>print(length(dat[dat >= 1.8 & dat < 2.0])) == tb[7]  # !?
>print(length(dat[dat >= 2.0 & dat < 2.2])) == tb[8]
>
>Best,
>///\\\///\\\///\\\///\\\///\\\///\\\///\\\///\\\
>Jose Claudio Faria
>UESC/DCET/Brasil
>joseclaudio.faria at gmail.com
>Telefones:
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>55(73)99966.9100 - VIVO
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>
>If you have software to deal with statistics, you have arms; if you
>have good software, you have arms and legs; if you have software like
>R, you have arms, legs and wings...
>the height of your flight depends only on you!
>
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>
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>
>______________________________________________
>R-help using 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.

-- 
Sent from my phone. Please excuse my brevity.