Select[list, crit] picks out all elements of list for which crit is True.
Select[list, crit, n] picks out the first n elements for which crit is True.
Example: Select[1,4,2,7,6, EvenQ] .
The object list can have any head, not necessarily List.
See The Mathematica Book: Section 2.2.7.
See also: Cases, Take, Drop.
Related package: Statistics`DataManipulation`.