[R] seq_len
Charilaos Skiadas
cskiadas at gmail.com
Sat Dec 8 15:52:34 CET 2007
On Dec 8, 2007, at 1:02 AM, Joe W. Byers wrote:
> In a post on R-devel, Prof Ripley add the following comment
> | > BTW, 1:dim(names)[1] is dangerous: it could be 1:0. That was the
> | > motivation for seq_len.
>
> I use the dim(names)[1] and dim(x)[2] along with length(x) with
> varying
> levels of frustration depending on the object which I am trying to get
> the dimensions. I found the reference to seq_len interesting since it
> is a function that I have never seen (probably just missed it reading
> the docs).
>
> I was hoping someone could expand on the benefits of seq_len.
I think that example says it all. But in simpler form, suppose x is a
vector, and you want to produce a regular sequence of integers of the
same length. What should happen i the vector x has length 0? Here's
the output of the two commands.
x<-numeric(0)
> y<-length(x)
> y
[1] 0
> 1:y
[1] 1 0
> seq_len(y)
integer(0)
Other than treating the edge case correctly, the only other advantage
of seq_len, that I am aware of, is that it is faster. Not sure how
often that ends up mattering though.
> Happy Holidays
> Joe
>
Haris Skiadas
Department of Mathematics and Computer Science
Hanover College
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