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

Mon Sep 24 21:00:58 CEST 2018

Dears,

Thank you for your contribution!

However, this function is important in a generic usage package for
frequency distribution tables: fdth (
https://cran.r-project.org/web/packages/fdth/index.html).

In this case, when I do not know in advance what the user data is, what is
the best option to avoid deviations as centuados as the example?

The data used in the example was sent to me from a teacher trying to
reproduce in class the table of a book.

Best,

///\\\///\\\///\\\///\\\///\\\///\\\///\\\///\\\
Jose Claudio Faria
UESC/DCET/Brasil
joseclaudio.faria at gmail.com
Telefones:
55(73)3680.5545 - UESC
55(73)99966.9100 - VIVO
55(73)98817.6159 - OI
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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!

2018-09-24 14:42 GMT-03:00 David L Carlson <dcarlson using tamu.edu>:

> Yes, I should have included that point. The cut() function "encourages"
> exact comparison of values by including the right= argument without a
> warning that this may create unexpected results. With truly continuous
> data, values falling exactly on the boundary would be rare.
>
> Most data arrives from instruments that measure to limited precision.
> Introductory statistics texts deal with this by distinguishing between
> "true" and "stated" class limits. Or, like Lyman Ott, recommend choosing
> the starting point interval such that "no measurement falls on a point of
> division between two intervals."
>
> ----------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77843-4352
>
> -----Original Message-----
> From: Jeff Newmiller <jdnewmil using dcn.davis.ca.us>
> Sent: Monday, September 24, 2018 10:41 AM
> To: r-help using r-project.org; David L Carlson <dcarlson using tamu.edu>; Jose
> Claudio Faria <joseclaudio.faria using gmail.com>; r-help using r-project.org
> Subject: Re: [R] cut{base}: is it a bug?
>
> "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:
> >55(73)3680.5545 - UESC
> >55(73)99966.9100 - VIVO
> >55(73)98817.6159 - OI
> >///\\\///\\\///\\\///\\\///\\\///\\\///\\\///\\\
> >
> >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!
> >
> >       [[alternative HTML version deleted]]
> >
> >______________________________________________
> >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.
> >
> >______________________________________________
> >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.
>

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