[R] Is k equivalent to k:k ?
Marcus Davy
MDavy at hortresearch.co.nz
Wed Dec 8 23:38:29 CET 2004
Bringing up an old topic on a small technicality.
In the help documentation on seq.
Value:
The result is of 'mode' '"integer"' if 'from' is (numerically
equal to an) integer and 'by' is not specified.
The arguement in seq specifying length also creates "double" which is not obvious in the wording, as "by" is not specified but
the object is double.
> typeof(seq(from=1, length=1))
[1] "double"
marcus
>>> Martin Maechler <maechler at stat.math.ethz.ch> 3/08/2004 3:15:45 AM >>>
>>>>> "Georgi" == Georgi Boshnakov <georgi.boshnakov at umist.ac.uk>
>>>>> on Mon, 2 Aug 2004 15:46:37 +0100 writes:
Georgi> Hi, I wonder if the following (apparent)
Georgi> inconsistency is a bug or feature.
a feature "of course".
Georgi> Since scalars are simply vectors of length one I
Georgi> would think that a and a:a produce the same result.
Why would you?
Have you read the documentation for ":" carefully?
{Part this topic, namely that a numeric constant such as "4"
is a "double" in R (but integer in S-plus since S+5.0)
should probably finally end up in the R FAQ ...
}
Regards, Martin Maechler
Georgi> For example,
>> identical(4.01,4.01:4.01)
Georgi> [1] TRUE
Georgi> However,
Georgi> identical(4,4:4)
Georgi> [1] FALSE
Georgi> and
>> identical(4.0,4.0:4.0)
Georgi> [1] FALSE
Georgi> A closer look reveals that the colon operator produces objects of different class, e.g.
a closer look wouldn't have been necessary had you read and
understood the documentation.
>> class(4)
Georgi> [1] "numeric"
>> class(4.0)
Georgi> [1] "numeric"
Georgi> but
>> class(4:4)
Georgi> [1] "integer"
>> class(4.0:4.0)
Georgi> [1] "integer"
Georgi> Georgi Boshnakov
Georgi> ------------------------------------------------------------------------------
Georgi> Dr Georgi Boshnakov tel.: +44 (0)161 200 3684
Georgi> Mathematics Department email: georgi.boshnakov at umist.ac.uk
Georgi> UMIST
Georgi> P O Box 88
Georgi> Manchester M60 1QD
Georgi> UK
Georgi> [[alternative HTML version deleted]]
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