Extract[expr, list] extracts the part of expr at the position specified by list.
Extract[expr, , , ... ] extracts a list of parts of expr.
Extract[expr, ... , h] extracts parts of expr, wrapping each of them with head h before evaluation.
Extract[expr, i, j, ... ] is equivalent to Part[expr, i, j, ... ].
The position specifications used by Extract have the same form as those returned by Position, and used in functions such as MapAt and ReplacePart.
You can use Extract[expr, ... , Hold] to extract parts without evaluation.
If expr is a SparseArray object, Extract[expr, ... ] extracts parts in the corresponding ordinary array.
See Section 2.4.2.
See also: Part, Take, PadLeft.
New in Version 3.