Message-ID: <6DA8FE3D-A1A3-4891-8DFA-40B26CF94854@xs4all.nl>
Date: 2017-02-18T20:35:03Z
From: Berend Hasselman
Subject: A strange arithmetic error in R (maybe a bug)
In-Reply-To: <686E9826-AE82-4C38-8831-1A12B1DEB00E@me.com>
> On 18 Feb 2017, at 05:18, T. Zhang <tz05 at me.com> wrote:
>
> Hello,
>
> Today I happened to notice a strange error in R. If you type (2.01-0.06)==1.95, output from R is ?FALSE?, which is wrong. But if you type (1.01-0.06)==0.95, output is ?TRUE?, which is correct. I tested this in two systems: R 3.3.2 in my iMac and R 3.2.0 on my school?s Linux server. Both gave same outputs. As shown in the following:
>
>> 2.01-0.06
> [1] 1.95
>> (2.01-0.06)==1.95 # should be TRUE; output is wrong
> [1] FALSE
>> 1.01-0.06
> [1] 0.95
>> (1.01-0.06)==0.95 # should be TRUE; output is correct
> [1] TRUE
>> (2.01-0.06)>1.95 # should be FALSE; output is correct
> [1] FALSE
>> (2.01-0.06)<1.95 # should be FALSE; output is wrong
> [1] TRUE
>
> Similar errors could be found with simple alterations of the above inputs, such as:
>> 5.533-5.412
> [1] 0.121
>> (5.533-5.412)==0.121 # should be TRUE; output is wrong
> [1] FALSE
>> 2.533-2.412
> [1] 0.121
>> (2.533-2.412)==0.121 # should be TRUE; output is correct
> [1] TRUE
>
> Could any of you test whether you have same outputs as mine? And does anyone know what is wrong with these? My guess is that R has a bug in processing double numbers. Thanks!
>
Not a bug. See the R FAQ section 7.31.
Berend Hasselman
> TZ
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