This is documentation for Mathematica 4, which was
based on an earlier version of the Wolfram Language.

Position

Position[expr, pattern] gives a list of the positions at which objects matching pattern appear in expr.

Position[expr, pattern, levspec] finds only objects that appear on levels specified by levspec.

Position[expr, pattern, levspec, n] gives the positions of the first n objects found.

Example: Position[1+x^2, 5, x^4, x^_] .

Position[expr, pattern] tests all the subparts of expr in turn to try and find ones that match pattern.

Position returns a list of positions in a form suitable for use in Extract, ReplacePart and MapAt. The form is different from the one used in Part.

The default level specification for Position is {0, Infinity}, with Heads -> True.

A part specification {} returned by Position represents the whole of expr.

Position[list, pattern, 1, Heads -> False] finds positions only of objects that appear as complete elements of list.

Level specifications are described in Section A.3.6.

See The Mathematica Book: Section 1.8.5, Section 2.1.7, Section 2.2.4 and Section 2.3.2.