R help - Dec 2007 - seq_len

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.

Happy Holidays
Joe

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