Cases
Cases[
, 
, ... 
, pattern] gives a list of the 
that match the pattern.
Cases[
, ... 
, pattern -> rhs] gives a list of the values of rhs corresponding to the 
that match the pattern.
Cases[expr, pattern, levspec] gives a list of all parts of expr on levels specified by levspec which match the pattern.
Cases[expr, pattern -> rhs, levspec] gives the values of rhs which match the pattern.
Example: Cases[
2, x, 4
, _Integer]
.
The first argument to Cases need not have head List.
Cases[expr, pattern, levspec, n] gives the first n parts in expr which match the pattern.
Level specifications are described in Section A.3.6.
See The Mathematica Book on the web: Section 2.3.2.
See also: Select, Position, ReplaceList, Collect.
Further Examples
