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

[David L Carlson]

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,
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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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