Generating Combinations

Every time I have to do this I "invent" a different way. Time to standardize. I suspect there is some default command I overlooked开发者_C百科 ready to do this, so I am sorry in advance if the question is too trivial.

What is the better (memory, performance) way to get:

 combinations[{1,2,3},2] = {{1,2},{1,3},{2,3}}

with arbitrary elements in the input list, of course.

Subsets[{1, 2, 3}, {2}]

is the built-in way.

Before Subsets was added as a core function, the Combinatorica function KSubsets was available.

Needs["Combinatorica`"]

KSubsets[{1, 2, 3}, 2]

(*  {{1, 2}, {1, 3}, {2, 3}}  *)

Combinatorica still provides additional functionality, such as NextKSubset:

NextKSubset[{1, 2, 3}, {1, 3}]

(*  {2, 3}  *)

This last function can be very helpful for memory management.