BUILT-IN MATHEMATICA SYMBOL

Cases

Cases[{e₁, e₂, ...}, pattern]
gives a list of the that match the pattern.

Cases[{e₁, ...}, pattern->rhs]
gives a list of the values of rhs corresponding to the that match the pattern.

Cases[expr, pattern, levelspec]
gives a list of all parts of expr on levels specified by levelspec that match the pattern.

Cases[expr, pattern->rhs, levelspec]
gives the values of rhs that match the pattern.

Cases[expr, pattern, levelspec, n]
gives the first n parts in expr that match the pattern.

Details and Options Details and Options

The first argument to Cases need not have head List.
Cases[expr, pattern:>rhs] evaluates rhs only when the pattern is found.
Cases uses standard level specifications:
n levels through n

Infinity levels through Infinity

{n} level n only

{n₁,n₂} levels through
The default value for levelspec in Cases is .
A positive level n consists of all parts of expr specified by n indices.
A negative level -n consists of all parts of expr with depth n.
Level consists of numbers, symbols and other objects that do not have subparts.
Level corresponds to the whole expression.
With the option setting Heads->True, Cases looks at heads of expressions, and their parts.
Cases traverses the parts of expr in a depth-first order, with leaves visited before roots.