pairs from a list

[Alan G Isaac]

Steven D'Aprano wrote:
> In fact, "fastest" isn't even a meaningful attribute. Does it mean:
> 
> * the worst-case is fastest
> * the best-case is fastest
> * the average-case is fastest
> * fastest on typical data
> * all of the above


I confess that it did not occur to me that there
might be an interesting distinction among these
cases for the question of how to get sequential
pairs from a list.  How would one draw these
distinctions in this case?

Thanks,
Alan Isaac

PS Just for context, the sequential pairs were
needed in a simulation, but my question was
primarily prompted by my surprise that the
approaches I looked at differed as much as they did.